How are we to understand these words of the Creed, “I believe in one God the Father?”
According to the Scriptures and the Apostolic Tradition, God the Father is the cause and origin, the “principle and source,” in the language of St Photius, of his Word (the Son) and of his Wisdom (the Holy Spirit). St Irenaeus expresses this with his celebrated image of the Father’s “two hands”:
It was not angels who made us… for God did not stand in need of them to accomplish what He had Himself determined beforehand should be done, as if He did not possess His own hands. For with Him were always present the Word and Wisdom, the Son and the Spirit, by whom and in whom, freely and spontaneously, He made all things, to whom also He speaks, saying, “Let Us make man after Our image and likeness.” (St Irenaeus, Against Heresies, IV.20.1)
God the Father is thus always with, and inseparable from, his Only-Begotten Son and his Holy Spirit for “God is love” (1Jo 4:8; see Q006, Q144), and love “is not self-oriented” (1Co 13:5). God is eternally in a perfect state of glory, unity, and communion.
St Basil the Great and St Gregory the Theologian teach that the unity of God is rooted in the person of the Father: there is one God because there is one Father. God is one because the essence of the three Persons is one, and God is one because the Father, from whom the Son is begotten and the Spirit proceeds, is one. The divine essence is therefore never an impersonal substance from which the Persons emerge: it exists only as the essence of the Father, communicated whole to the Son and to the Spirit. As St John of Damascus writes:
The Son is from the Father by generation, and the Holy Spirit is also from the Father, yet not by generation, but by procession. We know there is a difference between generation and procession, but the exact nature of this difference we cannot comprehend. All that the Son and the Spirit possess, even their very existence, they have from the Father. And unless the Father exists, neither the Son nor the Spirit exists. (St John of Damascus, Exact Exposition of the Orthodox Faith, I.8)
This, then, is the mystery of the Trinity: God the Father is eternally with his Word (the Only-Begotten Son) and his Spirit; they are uncreated and co-eternal, co-equal in that they belong together to the order of Creator, not of creature.
The mystery of the Holy Trinity may also be expressed thus: God is one in essence and triune in Persons, the Father, the Son, and the Holy Spirit, “the Trinity, one in essence and undivided,” as the Church confesses at every Divine Liturgy.
The counsel which St Cyril of Jerusalem gave his catechumens in the fourth century remains valid:
The Father, through the Son, with the Holy Spirit, gives every gift. The gifts of the Father are not one thing, those of the Son another, and those of the Holy Spirit yet another: there is one salvation, one power, one faith. There is one God, the Father; one Lord, His Only-Begotten Son; and one Holy Spirit, the Advocate. It is enough for us to know these things. Do not inquire curiously into His nature or substance… It is sufficient for our salvation to know that there is Father, Son, and Holy Spirit. (St Cyril of Jerusalem, Catechetical Lectures, 16.24)
