The Trinity
How can God be three and still be one?
"Now this is the Catholic faith: We worship one God in the Trinity and the Trinity in unity, without either confusing the persons or dividing the substance; for the person of the Father is one, the Son's is another, the Holy Spirit's another; but the Godhead of the Father, Son and Holy Spirit is one, their glory equal, their majesty coeternal" (Athanasian Creed: DS 75; ND 16).
Christians are baptized in the name of the Father and of the Son and of the Holy Spirit: not in their names, Cf. Profession of faith of Pope Vigilius I (552): . for there is only one God, the almighty Father, his only Son and the Holy Spirit: the Most Holy Trinity.
The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the "hierarchy of the truths of faith". . The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men "and reconciles and unites with himself those who turn away from sin". .
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". Dei Filius 4: . 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.
Jesus revealed that God is Father in an unheard-of sense: he is Father not only in being Creator; he is eternally Father by his relationship to his only Son who, reciprocally, is Son only in relation to his Father: "No one knows the Son except the Father, and no one knows the Father except the Son and any one to whom the Son chooses to reveal him." Mt 11-27.
Before his Passover, Jesus announced the sending of "another Paraclete" (Advocate), the Holy Spirit. At work since creation, having previously "spoken through the prophets", the Spirit will now be with and in the disciples, to teach them and guide them "into all the truth". Cf. Gen 1:2; Nicene Creed (); Jn 14:17, 26; 16:13. The Holy Spirit is thus revealed as another divine person with Jesus and the Father.
In order to articulate the dogma of the Trinity, the Church had to develop her own terminology with the help of certain notions of philosophical origin: "substance", "person" or "hypostasis", "relation" and so on. In doing this, she did not submit the faith to human wisdom, but gave a new and unprecedented meaning to these terms, which from then on would be used to signify an ineffable mystery, "infinitely beyond all that we can humanly understand". Paul VI, CPC # 2.
The Church uses (I) the term "substance" (rendered also at times by "essence" or "nature") to designate the divine being in its unity, (II) the term "person" or "hypostasis" to designate the Father, Son and Holy Spirit in the real distinction among them, and (III) the term "relation" to designate the fact that their distinction lies in the relationship of each to the others.
The Trinity is One. We do not confess three Gods, but one God in three persons, the "consubstantial Trinity". Council of Constantinople II (553): . The divine persons do not share the one divinity among themselves but each of them is God whole and entire: "The Father is that which the Son is, the Son that which the Father is, the Father and the Son that which the Holy Spirit is, i.e. by nature one God." Council of Toledo XI (675): :26. In the words of the Fourth Lateran Council (1215), "Each of the persons is that supreme reality, viz., the divine substance, essence or nature." Lateran Council IV (1215): .
The divine persons are really distinct from one another. "God is one but not solitary." Fides Damasi: . "Father", "Son", "Holy Spirit" are not simply names designating modalities of the divine being, for they are really distinct from one another: "He is not the Father who is the Son, nor is the Son he who is the Father, nor is the Holy Spirit he who is the Father or the Son." Council of Toledo XI (675): :25. They are distinct from one another in their relations of origin: "It is the Father who generates, the Son who is begotten, and the Holy Spirit who proceeds." Lateran Council IV (1215): . The divine Unity is Triune.
The divine persons are relative to one another. Because it does not divide the divine unity, the real distinction of the persons from one another resides solely in the relationships which relate them to one another: "In the relational names of the persons the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance." Council of Toledo XI (675): . Indeed "everything (in them) is one where there is no opposition of relationship." Council of Florence (1442): . "Because of that unity the Father is wholly in the Son and wholly in the Holy Spirit; the Son is wholly in the Father and wholly in the Holy Spirit; the Holy Spirit is wholly in the Father and wholly in the Son." Council of Florence (1442): .
"O blessed light, O Trinity and first Unity!" LH, Hymn for Evening Prayer. God is eternal blessedness, undying life, unfading light. God is love: Father, Son and Holy Spirit. God freely wills to communicate the glory of his blessed life. Such is the "plan of his loving kindness", conceived by the Father before the foundation of the world, in his beloved Son: "He destined us in love to be his sons" and "to be conformed to the image of his Son", through "the spirit of sonship". Eph 1:4-5, 9; Rom 8:15, 29. This plan is a "grace [which] was given to us in Christ Jesus before the ages began", stemming immediately from Trinitarian love. 2 Tim 1:9-10. It unfolds in the work of creation, the whole history of salvation after the fall, and the missions of the Son and the Spirit, which are continued in the mission of the Church. Cf. AG 2-9.
The whole divine economy is the common work of the three divine persons. For as the Trinity has only one and the same natures so too does it have only one and the same operation: "The Father, the Son and the Holy Spirit are not three principles of creation but one principle." Council of Florence (1442): ; cf. Council of Constantinople II (553): . However, each divine person performs the common work according to his unique personal property. Thus the Church confesses, following the New Testament, "one God and Father from whom all things are, and one Lord Jesus Christ, through whom all things are, and one Holy Spirit in whom all things are". Council of Constantinople II: . It is above all the divine missions of the Son's Incarnation and the gift of the Holy Spirit that show forth the properties of the divine persons.
Being a work at once common and personal, the whole divine economy makes known both what is proper to the divine persons, and their one divine nature. Hence the whole Christian life is a communion with each of the divine persons, without in any way separating them. Everyone who glorifies the Father does so through the Son in the Holy Spirit; everyone who follows Christ does so because the Father draws him and the Spirit moves him. Cf. Jn 6:44; Rom 8:14.