The Best Guide for Understanding the Trinity

Faith in the Trinity rests on God’s revelation of himself in the economy of salvation. We do not have access to the Trinity outside what God revealed to us by sending his own Son and giving us his Holy Spirit. This point is crucial. Trinitarian faith is distinct from experiences that begin by observing nature, or studying cultural phenomena, or that start from arguments or human introspection. It rests exclusively on the gift that God makes when he enables believers to know him in faith. The revelation of the Trinity is accomplished by the coming of God himself into human history: God so loved the world that he gave his only Son (John 3:16); God’s love has been poured into our hearts through the Holy Spirit who has been given to us (Rom 5:5).

The Trinity is a mystery of faith in the strict sense, one of the “mysteries that are hidden in God, which can never be known unless they are revealed by God.” To be sure, God has left traces of his Trinitarian being in his work of creation and in his revelation throughout the Old Testament. But his inmost Being as Holy Trinity is a mystery that is inaccessible to reason alone or even to Israel’s faith before the incarnation of God’s Son and the sending of the Holy Spirit (CCC §237).

Two aspects of this affirmation merit special attention. First, the believer’s knowledge of the Trinity rests on the revelation that takes place in the words and in the historical events to which the words are connected. These events are the incarnation of the Son of God and his life in our human condition, as well as the sending of the Holy Spirit to the Church at Pentecost. This manifestation of the Trinity is different from other forms of revelation (for example, the revelation that God can make simply by the interior inspiration of the mind of prophets), because the revelation of the Trinity takes place in events manifested to human eyes.

Second, in these events God himself comes. God is not only at the origin of these events, but he also gives himself in them. Thus, in the incarnation, the Son of God in person becomes human and, by his life and his offering on the cross, he obtains salvation through love of his Father and through love of humankind. Similarly, at Pentecost, the Holy Spirit in person is given and comes to dwell in the heart of believers. And when, by the grace of the Holy Spirit, believers receive Jesus as the Son of God, the Father himself comes to dwell in their hearts, as Jesus promised: “If a man loves me, he will keep my word, and my Father will love him, and we will come to him and make our home with him” ( John 14:23).

In the events of salvation, God the Trinity gives not merely “some thing,” but rather he gives himself: God the Father sends his Son and pours out his Holy Spirit. These two aspects (God is revealed in historical events, and in them he really gives himself to believers) are at the center of the revelation of the Trinity. They constitute a fundamental and characteristic trait of the evangelical faith that distinguishes it from other forms of knowledge and of religious experience.

The Liturgy

The liturgy of the Church—in particular the celebration of baptism, confirmation, and the Eucharist—offers the best guide for understanding the depth of Trinitarian faith: in the paschal mystery of Christ, the Church recognizes and celebrates God the Trinity. The liturgy enables believers to receive the Trinitarian mystery and to live it. Concretely, it is through the liturgy that Christians enter into the mystery of God the Trinity and find the light to live out their lives with God. In the liturgy, the Church proclaims the Word that reveals the mystery of God; she celebrates God and is united to him. The depth of Trinitarian faith can be understood within the home that is the celebration of the Eucharist. Through the Eucharist, according to Unitatis redintegratio §15,

The faithful, united with their bishop, have access to God the Father through the Son, the Word made flesh, who suffered and has been glorified, and so, in the outpouring of the Holy Spirit, they enter into communion with the most holy Trinity, being made “sharers of the divine nature” (2 Pt 1:4).

The Eucharist, which fortifies one’s union with Christ, strengthens and nourishes the gift obtained by baptism and confirmation: believers are united to the Father through the Son, in the Holy Spirit. When they commune in the flesh of Christ and receive the Holy Spirit, believers are united to the Father: they are a “new creation” (Gal 6:15). The fruit of the sacraments is not only of the moral order, but rather it concerns first and foremost the being of believers.

By the coming of the Son of God and the gift of the Holy Spirit, believers are renewed and transformed in their very being. The eternal Son of the Father is born in time in order to give us a share in his own life: “God was made man, so that man might be made God” (St. Athanasius). The sacraments of faith, which unite us to Christ by the gift of the Holy Spirit, obtain for us a new being destined to bloom in moral sanctity. “Therefore, if any one is in Christ, he is a new creation” (2 Cor 5:17). The Eucharist gives a participation in the very mystery of the Trinity: it is “divinization,” in which we become “partakers of the divine nature” (2 Peter 1:4).

Faith in the Trinity is intimately connected to this “new creation” that the sacraments effect. By receiving the Holy Spirit, by communing in Christ, believers enter into the divine life. They are led to the Father by the divine power of the Son and Holy Spirit who renew them interiorly. Thus, faith in the divinity of Christ, who is the only-begotten Son of the Father, and in the divinity of the Holy Spirit, who is the Spirit of the Father and the Son, is expressed in an exemplary manner in the sacraments that bring about communion in the divine life.

The “stake,” so to say, of faith in the Trinity is salvation itself, the participation of the Church in the Trinitarian life. The revelation of the Trinity is ordered to this participation in the Trinitarian mystery that constitutes the Church. The structure or “disposition” of this revelation is well expressed by the collect of the feast of the Holy Trinity:

God the Father, you who by sending into the world the Word of truth and the Spirit of sanctification have manifested to men your admirable mystery, give us in confessing the true faith to recognize the glory of the eternal Trinity, and to adore the Unity in the power of majesty.

The mystery of God has been revealed to us by the Father himself. This revelation is accomplished by the sending of the Son and of the Holy Spirit. By designating the Son as “Word of truth,” the prayer of the feast of the Holy Trinity signifies that the Son is sent into the world in order to make known the mystery of God. It belongs to the “Word” as such to make manifest and to reveal the true face of God, by a knowledge that transforms hearts.

By designating the Holy Spirit as the “Spirit of sanctification” (cf. Rom 1:4), the Church signifies that the revelation of God is accomplished in the gift of new life that is obtained by the outpouring of the Holy Spirit. The revelatory and sanctifying action of the Son and of the Holy Spirit finds its origin in the Father himself, because the Father is the Source of the sending of the Son and of the Holy Spirit, in such a way that the Son and the Holy Spirit reveal the mystery of the Source itself: the mystery of the Father.

This prayer likewise indicates the two aspects of our understanding of the mystery of God the Trinity in faith: the relations of the persons and their unity of being. The relations are signified by the theme of mission: the Son and the Holy Spirit come forth from the Father who “sends” them. The unity is especially associated with the divine power. The actions of the Son and of the Holy Spirit manifest their equality in power with the Father. The Son and Holy Spirit reveal, sanctify, and save. They perform actions that God alone can accomplish. Their divinity is revealed particularly in this power: the works of God make visible “his eternal power and deity” (Rom 1:20).

The prayer of the feast of the Holy Trinity also signifies that the sending of the Son and of the Holy Spirit, which takes place in time, leads the Church to lift up its gaze toward the mystery of God who is above time, that is to say to recognize “the glory of the eternal Trinity.” The word glory evokes the transcendent mystery of God the Trinity, in all its “weight,” manifested by Christ and by the gift of the Holy Spirit, and recognized by the Church’s faith and love. In the teaching of the Fathers of the Church about the Trinity and about Christ, the divine glory is associated with manifestation, with light and its rays, with renown, with royalty and power; hence, the word “glory” (gloria) has come to designate the divine nature proper to the Father, Son, and Holy Spirit.

The liturgy of the Church especially proclaims the glory of the Trinity in the “doxologies” (from the Greek doxa: glory). The doxology constitutes a special form of praise. In the strict sense, one calls “doxologies” the formulas in which the word “glory” is attributed to God by means of a turn of phrase expressing possession. The doxologies do not regard an action of God, as do other liturgical forms of expression, but rather they are focused directly on the glory of God and his sanctity. They do not express a wish, but rather they declare the reality of God.

One finds a good example in Revelation 5:13: “To him who sits upon the throne and to the Lamb be blessing and honor and glory and might for ever and ever!” One observes here three fundamental elements that constitute a doxology. First, the doxology names the one to whom it acknowledges glory: here, God who sits on the throne, and the Lamb. Second, it proclaims that glory belongs to him. Third, it includes a phrase that signifies eternity (“for ever and ever”). One can add a fourth element: the “Amen” pronounced by the four living creatures (Rev 5:14).

The “lesser doxology” (“lesser” on account of its brevity) that concludes the liturgical prayer of the psalms offers a familiar example: “Glory to the Father, and to the Son, and to the Holy Spirit.” This doxology reflects the baptismal formula conferred “in the name of the Father and of the Son and of the Holy Spirit” (Matt 28:19). In the baptismal formula, the “name” of the Father, Son, and Holy Spirit is much more than a “word.” By invoking the “name” of the Father, Son, and Holy Spirit, one signifies the tri-personality of God who manifests himself to human beings, who enables them to enter into a covenantal relationship with him, and to whom one can address oneself.

The “name,” in the singular, also suggests the unity of the Father, Son, and Holy Spirit. The phrase “in the name of ” does not mean “by the mandate of ” but rather indicates that, by the action of the Father, Son, and Holy Spirit, the baptized pass from the domination of sin to the sovereignty of the triune God whom they can invoke in a personal relationship, in view of the communion with the Son in the Kingdom of his Father, through the Holy Spirit. In reference to the baptismal formula, the Trinitarian doxology expresses the equal greatness of the Father, Son, and Holy Spirit.

They are not three glories, nor three portions of glory shared among three persons, but it is the same undivided glory that one proclaims in the Three. To acknowledge in the Son and Holy Spirit the same glory as in the Father, is to confess their equal divinity. At the same time, the doxology signifies the personal distinctiveness of the Father, Son, and Holy Spirit: they have the same glory but they are not blended.

The Gloria, the “greater doxology” chanted in the Mass, likewise expresses this shared dignity of the Son and Holy Spirit with the Father, in their distinction: “You alone are the Most High: Jesus Christ, with the Holy Spirit, in the glory of the Father. Amen.” And the doxology that concludes the Eucharistic prayers renders glory to the Father through the Son, Christ Jesus, in the Holy Spirit. The doxologies, either in the form of a “co-ordinate” address (Glory to the Father, and to the Son, and to the Holy Spirit) or following a “mediatorial” pattern (Glory to the Father, through the Son, in the Holy Spirit), are a central expression of Trinitarian faith. The former (“co-ordinate” address) ranks the three persons together as equal, while the latter (“mediatorial” pattern) makes clear the order of the divine persons in the economy of salvation.

Let us listen to the witness of an ancient Christian writing, the Martyrdom of St. Polycarp, which presents a beautiful Trinitarian doxology. In this writing, the holy martyr addresses this prayer to God the Father:

For this, and for all else besides, I praise thee, I bless thee, I glorify thee; through our eternal High Priest in Heaven, thy beloved Son Jesus Christ, by whom and with whom be glory to thee and the Holy Spirit, now and for all ages to come. Amen.

Other ancient writings present such Trinitarian doxologies. Thus, for example, the Apostolic Tradition of Hippolytus of Rome: “To you be glory, to the Father and to the Son with the Holy Spirit in the holy Church, both now and for ever and into all the ages of ages.” In this doxology, the Father, Son, and Holy Spirit are “enumerated,” so to say, each in his place but on the same level. This means that the Three have the same dignity and belong to the same order: that of divine persons. Sometimes also, in the doxology, the Father, Son, and Spirit are united under the name “Trinity.”

An example is found in this antiphon of the first vespers of the feast of the Holy Trinity: “Glory to you, equal Trinity, one Deity, from before all ages, and now and forever more.” Trinitarian doctrine—the exposition of faith in the Trinity—makes explicit what the doxologies express under a liturgical form that always remains primary.

At times one finds opposed to Trinitarian faith a rather superficial argument: the word “Trinity” is absent from the Bible; the Trinity is therefore unscriptural. Certainly, the word Trinity only appears later, in Greek (trias) from the second century and in Latin (trinitas) toward the beginning of the third century, in Christian authors. But the reality signified by the word “Trinity” is exactly that which the baptismal formula and the doxologies—themselves found in Scripture—express: the Father, Son, and Holy Spirit are “co-numbered” or “numbered together,” they are mentioned or “counted one with the other” (the Father, and the Son, and the Holy Spirit) because they belong to the same order of reality.

The creed likewise repeats this baptismal and doxological order of the divine persons. The Church professes her faith in the same way that she renders glory: “We believe in the Father, and in the Son, and in the Holy Spirit.” The Catechism of the Catholic Church (§249) explains:

From the beginning, the revealed truth of the Holy Trinity has been at the very root of the Church’s living faith, principally by means of Baptism. It finds its expression in the rule of baptismal faith, formulated in the preaching, catechesis and prayer of the Church. Such formulations are already found in the apostolic writings, such as this salutation taken up in the Eucharistic liturgy: “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all” (2 Cor 13:13; cf. 1 Cor 12:4–6; Ep 4:4–6).

In the Holy Spirit that they receive, the baptized are conformed to the Son and they become children of the Father. The baptismal formula (which animates preaching, the confession of faith, catechesis, and prayer), like the doxologies, does not express solely the equal divine dignity of the Father, Son, and Holy Spirit. It also indicates that this divinity belongs to the Three according to an order: the Father, and the Son, and the Holy Spirit. This order means that the Three are distinct. The Father is the Source of the Son and of the Holy Spirit. In the same way that the Father has sent his Son and his Holy Spirit in the economy of salvation, the Father begets his Son from all eternity and eternally “breathes” the Holy Spirit.

Thus, the baptismal formula and the doxologies express the divine unity of the Three and their personal distinction, according to an order. This order is well-signified by the final doxology of the Eucharistic prayers: “Through him, with him, in him, in the unity of the Holy Spirit, all glory and honor is yours, almighty Father, for ever and ever. Amen.” Here, it is necessary to pay attention to the interaction of prepositions and conjunctions. In the baptismal formula, the conjunctions “and”—“and” emphasize the equal dignity of the Father, Son, and Holy Spirit (“co-ordinate” mention of the three persons).

In the doxology of the Eucharistic prayers, the prepositions “through”— “in” signify the same order of the Three, but by indicating more precisely the distinct place of the Father, Son, and Holy Spirit in the economy of salvation (“mediatorial pattern”): glory is rendered to the Father “through the Son” and “in the Holy Spirit.” Christian liturgical prayer is thus addressed to the Father, through the Son, and in the Holy Spirit. The explanation of St. Basil of Caesarea (fourth century) in On the Holy Spirit is illuminating:

If we are illumined by divine power, and fix our eyes on the beauty of the Image of the invisible God, and through the Image are led up to the indescribable beauty of its Source, it is because we have been inseparably joined to the Spirit of knowledge. He gives those who love the vision of truth the power which enables them to see the Image, and this power is Himself. He does not reveal it to them from outside sources, but leads them to knowledge personally, “No one knows the Father except the Son” (Matt 11:27), and “No one can say Jesus is Lord except in the Holy Spirit” (1 Cor 12:3).

The Holy Spirit sanctifies the baptized by his “illuminating power” in procuring for them the gift of living faith. This illumination enables one to know the radiance of the majesty of the Son, through whom one attains to contemplation of the Father. The transforming illumination of faith is received in the Holy Spirit. It is “from within” the Spirit that the baptized know the Son, through whom they are led to the Father.

St. Irenaeus of Lyons (second century) already explained this in similar terms in his Against Heresies: “Here is, according to the presbyters, the disciples of the apostles, the gradation and arrangement of those who are saved, and the steps by which they advance: they ascend through the Spirit to the Son, and through the Son to the Father.” St. Basil of Caesarea summarizes his account in On the Holy Spirit by noting two ways to consider the mystery of the Trinity:

The way to divine knowledge ascends from one Spirit through the one Son to the one Father. Likewise, natural goodness, inherent holiness and royal dignity reaches from the Father through the Only-Begotten to the Spirit.

St. Basil sums up here the twofold path of our approach to the Trinitarian mystery. The first path is that of our experience. This path begins with the Holy Spirit and, in the Son, leads to the Father. “For our mind, enlightened by the Spirit, looks upon the Son, and in Him, as in the Image, beholds the Father.” Under this aspect, the Holy Spirit is in a certain way “the closest to us,” the one who is most intimate to believers because he is poured forth in their hearts. The Holy Spirit is Gift in person: it is in him that believers are able to know the Son and to have access to the Father. In baptism, believers are consecrated to the Father through the Son, in the Holy Spirit who accomplishes interiorly their regeneration.

The second path is that of the order of the divine life at the heart of the Trinity. This is the order of origin in God himself. This path begins from the Father. The Father is the Source who communicates the fullness of divinity to the Son (this is the eternal begetting) and to the Holy Spirit (this is the eternal “spiration” of the Holy Spirit). The one divine nature is possessed by the Three according to an order: Father, and Son, and Holy Spirit. According to St. Athanasius, the action of the Trinity in our world reflects this same order: “The Father does all things through the Word in the Holy Spirit.” We likewise find here the order of sending: the Father sends his Son and his Spirit. The Father who is the Source in the eternal Trinity (this is the order of the reality in God himself, which the order of sending reflects) is also the end to which the Holy Spirit and the Son lead believers (this is the order of experience and of baptismal grace).

Biblical Paths

In the New Testament, the manifestation of the Father, Son, and Holy Spirit is directly connected to the gift of new life by grace: when the New Testament speaks of the Trinity, it speaks of the salvation of human beings; and when it speaks of salvation, it speaks of the Trinity. We will present certain aspects of the teaching of the New Testament in the following chapters of our book on The Trinity. It is necessary here, however, to recall this: to explore the witness of the revelation of the Trinity in the New Testament does not consist in a simple inventory of biblical verses. It is necessary first and foremost to survey the profound movement of revelation, understood as a whole in its various harmonies. The New Testament offers many complementary “paths” for understanding the revelation of the Trinity. We will briefly consider two of them here.

The first path begins with the human life of Jesus in order to lead us to his passion and his glorious exaltation that reveal the Trinity to us. This path shows that the Trinity is fully manifested at the end of the events of the human life of Jesus. Revelation finds its culminating point in the paschal mystery of Christ that reveals the Trinity. The discourse of the apostle Peter at Pentecost offers us an example (Acts 2:14–36). This apostolic preaching is addressed to the Jews of Jerusalem.

St. Peter explains that “Jesus of Nazareth, a man attested to you by God with mighty works and wonders and signs which God did through him in your midst . . . God raised him up, having loosed the pangs of death” (Acts 2:22–24); and a little further on: “This Jesus God raised up, and of that we are all witnesses. Being therefore exalted at the right hand of God, and having received from the Father the Holy Spirit who was promised, he has poured out this which you see and hear” (Acts 2:32–33). St. Peter concludes: “Let all the house of Israel therefore know assuredly that God has made him both Lord and Christ, this Jesus whom you crucified” (Acts 2:36).

In this preaching, St. Peter begins with the man Jesus (“this Jesus”) and with what Jesus accomplished, then he recalls his death on the cross, in order to lead to the proclamation of his glorious resurrection. The life of Jesus culminates in his exaltation. St. Peter underscores the newness that this exaltation brings. The resurrection is an event in which three agents act: Jesus, God (ho Theos, identified as the Father), and the Holy Spirit. The Three are named in their distinction. The paschal exaltation of Jesus places in full view his vivifying power and his unity with the Father: “God has made him both Lord and Christ.”

To say that Jesus is Lord (Kurios) is to acknowledge in him a dignity comparable to that of God. This name “Lord,” which is connected to the worship that Christians render to Christ, expresses the faith of Easter. In his sovereignty, Jesus possesses the prerogatives of God; he shares in the divine condition of his Father: “The Lord said to my Lord, Sit at my right hand” (Acts 2:34). This citation of Psalm 110:1 shows that the glorified Jesus occupies a unique place: he is with the Father in the most profound divine intimacy. St. Paul expresses this in a comparable manner when he explains having received the mission of announcing the Gospel of God “concerning his Son, who was descended from David according to the flesh and designated Son of God in power according to the Spirit of holiness by his resurrection from the dead, Jesus Christ our Lord” (Rom 1:3–4). His glorious resurrection manifests Jesus as Son in the power of the Holy Spirit. The name “Son” expresses here the most profound unity of Jesus with his Father, a properly divine unity that the exaltation of Jesus brings into broad daylight.

In the first discourse of St. Peter on Pentecost, the Father is present under the name of “God.” The Father has acted through Jesus, he has delivered Jesus from death and exalted him to his right hand. As regards the Holy Spirit, he appears as the paschal Gift par excellence. The Holy Spirit is poured out by the exalted Jesus: the giving of the Spirit is the fruit of the exaltation of Jesus. Put otherwise: the glorious exaltation shows Jesus as the Giver of the Holy Spirit (he “poured out” the Holy Spirit) because, having received the fullness of the Holy Spirit, he is in the glorified state in virtue of which he abundantly pours out this same Spirit. And it is in the Spirit of Pentecost that St. Peter proclaims the exaltation of Christ Jesus and his unity with the Father.

One can understand this teaching in the following way. It is God who pours out the Spirit. To pour out the Spirit is a divine privilege. God is in heaven; in order to pour out the Spirit, it is necessary to be where God is, and this is precisely what the paschal exaltation confers on the humanity of Jesus: the exalted Jesus is in heaven and, in his glorified humanity at the right hand of the Father, he exercises the divine prerogative that consists in pouring out the Spirit. The ascension of Christ manifests his filial divinity and enables his humanity to rejoin the throne that his divinity never left, and from where the Spirit is now poured out in abundance.

The exaltation of Christ procures us salvation inasmuch as “being established in his heavenly seat as God and Lord, he sends down divine gifts upon men.” (Aquinas, ST, III, q. 57, a. 6). This reveals an essential trait of Jesus as Christ, Lord, and Son of God: he pours out the Holy Spirit. The vision that St. Stephen receives at the moment of his martyrdom offers us an icon of this: “He, full of the Holy Spirit, gazed into heaven and saw the glory of God, and Jesus standing at the right hand of God(Acts 7:55). The glorious resurrection of Jesus thus manifests the Trinity: it shows the intimacy (unity) and the distinction of the Three in their saving action. Raised up by the Father, Jesus pours out the Spirit. And in the Spirit, believers are led to contemplation of the exalted Son beside his Father.

The events of Easter (passion, resurrection, ascension, Pentecost) thus provide a fundamental light for understanding the profound identity of Jesus and for discovering, in Jesus, the mystery of the Trinity. Under this aspect, the exaltation of Jesus and the paschal outpouring of the Holy Spirit constitute the center of the revelation of the Trinity. “The sending of the person of the Spirit after Jesus’ glorification (cf. John 7:39) reveals in its fullness the mystery of the Holy Trinity” (CCC §244).

In this first approach, we have focused our attention on the Pasch of Jesus. But the New Testament equally shows that the Holy Spirit is superabundantly present in Jesus from the beginning. The Gospels display in particular the active presence of the Holy Spirit at the baptism of Jesus. When Jesus is baptized, the Holy Spirit descends upon Jesus, he “remains” on him (John 1:32), and the Father declares that Jesus is his “beloved Son” (Mark 1:11; Matt 3:17). The Gospels’ witness to the baptism of Jesus present certain differences, but they converge on a fundamental affirmation: the kingdom of God comes through Jesus and in Jesus, by virtue of the relation of sonship that Jesus has with God his Father, in the power of the Holy Spirit.

The baptism of Jesus, which has profoundly inspired Christian iconography, is a manifestation of the Trinity. However, since the first centuries of Christianity, the episode of Jesus’s baptism has suggested to certain misguided readers that Jesus became the Son at the moment of his baptism, or that he only received the Holy Spirit when the Spirit descended upon him “like a dove.” For this reason, the best theological tradition insisted that the humanity of Jesus was completely filled with the Holy Spirit from the first instant of his conception. This is the teaching of the Church: “From his conception, Christ’s humanity is filled with the Holy Spirit, for God ‘gives him the Spirit without measure’ (John 3:34)” (CCC §504).

In light of this teaching, it is necessary to understand that the fullness of the Holy Spirit was manifested at the baptism of Jesus for the reason that “it is from this moment that he began to pour out his grace on others” (Aquinas, Commentary on the. Sentences, Bk. I, dist. 16 q. I, a. 3) by his ministry of salvation.

Put otherwise, at the baptism of Jesus, the Holy Spirit descends upon Jesus “for us and for our salvation,” that is to say in order to show that Jesus, the Son of the Father, has been sent to us as Savior. The baptism of Jesus takes place at the beginning of his ministry. It manifests the fullness of the Holy Spirit with which the humanity of Jesus was filled from his conception. The words of the Father and the sign of the Spirit thus reveal Jesus as Messiah at the beginning of his public activity. The baptism of Jesus is a manifestation, an epiphany.

The liturgy of the Church signifies this very well by associating the baptism of Jesus with his epiphany and with the sign of Cana:

Three mysteries mark this holy day: today the star leads the Magi to the infant Christ; today water is changed into wine for the wedding feast; today Christ wills to be baptized by John in the river Jordan to bring us salvation (antiphon of the Magnificat at the second vespers of the feast of Epiphany).

Similarly, at the very beginning of the human existence of Jesus, the action of the Holy Spirit (who forms the body of Christ in the womb of the Virgin Mary) reveals that Jesus is the true Son of God, come in a human nature like ours: “The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God” (Luke 1:35). The conception of Jesus by the Holy Spirit shows that Jesus is truly the Son of God.

The passages of the New Testament that start from the filial divinity of Jesus and from his preexistence offer a second “point of entry” for understanding the revelation of the Trinity. Christ Jesus, who exists in the “condition of God” (Phil 2:6), humbled himself for us in the incarnation and in obedience unto death. St. John designates Christ Jesus as the “Word” who “was with God” and “was God” from the beginning (John 1:1–2), the “only begotten Son, who is in the bosom of the Father” ( John 1:18) and who was “sent” by the Father into our world (John 3:17). Jesus “comes” into the world, he is sent here by his Father. The theme of coming and of sending indicates the preexistence of Jesus who comes from on high. “Before Abraham was, I am” ( Jn 8:58).

Jesus enters into the world by a voluntary action that he exercises with his Father. Following this second “point of entry,” the New Testament makes clear that the divinity of Jesus, from which the Holy Spirit is inseparable, is found at the root of all that Jesus does and says. Jesus is not only an admirable prophet, but rather he is the incarnate Son of God, sent by his Father; it is in him and through him that the Holy Spirit is poured out. The Trinity does not appear only at the resurrection of Jesus. It is the source that, from the beginning, enlightens the origin of the human life of Jesus, then his ministry, his salvific passion, and his glorious resurrection. The mystery of the divine identity of Jesus, in his relation to the Father and to the Spirit, unveils the profound meaning of Christmas and of Easter.

The one who is born of the Virgin Mary, through the action of the Holy Spirit, is the Son of God in person. The one who dies on the cross is the Son of God come to save humankind by his offering to the Father. From the paschal mystery of Christ, that is to say from the glorious unity of the Son with his Father, flows the Holy Spirit who is poured out in the Church. Thus, through the incarnate Son, who died, rose, and is glorified, in the outpouring of the Holy Spirit, believers enter into communion with the Father. This is the faith in the Trinity that enables one to understand the meaning of the events of the New Testament: “When the time had fully come, God sent forth his Son” (Gal 4:4); “God has sent the Spirit of his Son into our hearts, crying, ‘Abba! Father!’” (Gal 4:6).

Whatever the manner of approaching the Trinitarian faith, the gift of the Holy Spirit furnishes the key. It is the Holy Spirit who gives entrance into the mystery of the Son and his Father. The experience of the gift of the Spirit is especially highlighted by St. Paul. St. Paul presents the Christian life as a participation in Christ, a life with Christ. By baptism, believers are “buried” with Christ, in order to live with him in a new life, “as Christ was raised from the dead by the glory of the Father” (cf. Rom 6:1–11).

This union with Christ who died and is risen is procured by the Holy Spirit: the Spirit of God comes to “dwell” in believers; by receiving this Spirit, believers belong to Christ and are conformed to him. The new life “in Christ” is a life “in the Spirit” and “by the Spirit” (cf. Rom 8:1–17): as St. Paul says, “be filled with the Spirit” (Eph 5:18). The Spirit unites believers to Christ, he enables them to become children of God, and he thereby leads them to the Father: “You have received the spirit of sonship. When we cry, ‘Abba! Father!’ it is the Spirit himself bearing witness with our spirit that we are children of God” (Rom 8:15–16).

We find here the path of life of the baptized that we have sketched above with St. Irenaeus of Lyons and St. Basil of Caesarea. The gift of the Spirit obtains union with Christ and leads human beings to the Father. “Through him [Christ] we both have access in one Spirit to the Father” (Eph 2:18). It is in the Holy Spirit that faith in the Trinity is received, and it is in the Holy Spirit that this faith models Christian existence.

Let us summarize these first elements we have discussed. On the one hand, at the end of the earthly life of Jesus, the events of Easter manifest the Trinity in a magnificent way. In the Spirit poured out after the resurrection of Jesus, believers proclaim the divine glory of the Son with his Father.

On the other hand, from the beginning, it is faith in the Trinity that enables one to understand the profound meaning of the Incarnation, and then of Easter and of Pentecost: the Father sends his Son and he sends his Spirit. Between these two approaches, there is not a rupture but rather a continuity: they form, as it were, a circle. The loftiest teaching on the Trinity receives its light from faith in the resurrection of Jesus; and faith in the Trinity illumines in its turn the identity of Jesus, his life among human beings, his death, and his resurrection, as well as the action that Jesus continues to accomplish today in his Church.

The teaching of scripture concerning the Trinity is, at the same time, simple and difficult. It is simple, because it shows the Father, Son, and Holy Spirit in their unity and in the relations revealed by their action of salvation on behalf of humankind. The Trinity is a mystery of communion. “You see the Trinity if you see charity” (Augustine, On the Trinity). But this teaching is also difficult. It demands an attentive listening and it calls for an understanding in faith. It invites a contemplation of the Trinity that goes beyond what we can comprehend. St. Augustine observed in Letter 137 on the subject of holy Scripture:

The very style in which Scripture is composed is accessible to all, though very few can enter deeply into it. Like a close friend, it speaks without pretense those clear ideas it contains to the heart of the unlearned and of the learned. It does not exalt those things that it conceals in mysteries with a proud language to which the sluggish and untrained mind dares not approach, as a poor man dares not approach a rich one, but invites all with its lowly language. And it not only feeds them with the evident truth but also exercises them with the hidden truth, though it has the same truth in clear matters as in hidden ones. But so that obvious truths do not become boring, the same truths are again desired as concealed, and as desired are in a sense refreshed, and as refreshed they are taught with sweetness. By these, evil minds are salutarily corrected, little minds are fed, and great minds are delighted.

Scripture’s manner of speaking is accessible to all: it is not esoteric. But to grasp its profundity is difficult. St. Augustine notes two aspects. On the one hand, Scripture “nourishes” the faith of all believers by words in which the mystery is expressed in a clear and manifest way. On the other hand, by its more difficult words, Scripture “exercises” the understanding of more advanced believers; they refine their mind in the study of the truth. To be sure, all that is necessary for salvation is expressed somewhere in a clear and manifest manner. In any case, the mystery remains beyond the mastery of our intelligence: it offers itself to a contemplation practiced in humility. Trinitarian theology is a spiritual exercise.

EDITORIAL NOTE: This is an excerpt of Chapter 1 of The Trinity: An Introduction to Catholic Doctrine on the Triune God courtesy of The Catholic University Press of America, ALL RIGHTS RESERVED.

Featured Image: Francesco Pesellino and Fra Filippo Lippi and workshop. The Pistoia Santa Trinità Altarpiece, 1455; Source: Wikimedia Commons, PD-Old-100.


Gilles Emery

Gilles Emery, a Dominican priest of the Swiss province of Preachers, is professor of dogmatic theology at the University of Fribourg, Switzerland. He is the author of The Trinity: An Introduction to Catholic Doctrine on the Triune God.

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