*This is my mini-essay I just turned in for my mid-term assignment for my theology class at Princeton Theological Seminary (I wrote this quickly, so take it for what it is).
God is one, the Father in the Son, the Son in the Father with the Holy Spirit . . . true enhypostatic Father, and true enhypostatic Son, and true enhypostatic Holy Spirit, three Persons, one Godhead, one being, one glory, one God. In thinking of God you conceive of the Trinity, but without confusing in your mind the Father, the Son and the Holy Spirit. The Father is the Father, the Son is the Son, the Holy Spirit is the Holy Spirit, but there is no deviation in the Trinity from oneness and identity.
Even as Epiphanius wrote these words back in the 4th century during the patristic period of the early church, what he writes sounds less like an argument or clarification about the tri-unity of God and more like a prayerful confession he is crying out as he contemplates upon the depth dimension and ineffable reality of who the Christian God is as revealed in the dearly beloved Son. In kind, the rest of this brief essay will attempt to explicate how the Christian God can be both one and three, and how his oneness and threeness mutually implicate the other in both simplicity and multiplicity.
Epiphanius’ Triune ‘confession’ while terse and representative of a statement of faith (so to speak), at the same time suggests something more profound and more fruitful towards even a modern articulation of Trinitarianism. In other words, what Epiphanius’ statement suggests is corollary with an earlier contemporary of his in regard to understanding God as Triune; Athanasius is popular for noting that it is better to “signify God from the Son and call him Father, than to name God from his works alone and call him Unoriginate.” In other words, what has become more accepted and dominant in attempting to articulate a Christian Doctrine of God vis-à-vis a Doctrine of the Trinity, is to think from the ‘economic Trinity’ (oikonomia) back to the ‘immanent’ or ‘ontological Trinity’. And this move takes us back to people like Athanasius, Epiphanius, et al., and beyond what became the popular mode for articulating a Doctrine of God in the Medieval period, which was to attempt to speak of God as ‘one’ (de Deo uno) as a separate article from God being ‘three’ (de Deo trino). In other words, what Medieval theology, scholastic theology tended to do was to employ philosophical concepts about God (like Aristotle’s ‘Actual Infinite’ or Plato’s ‘Pure Being’ etc.), which was not commensurate with trying to articulate who God was as one God (ousia) shaped by an eternal communion (perichoresis) of the three persons (hypostaseis) as revealed in Jesus Christ. Fred Sanders writes:
. . . There was a traditional scholastic sequence, deriving from Aquinas (who in this departed from Lombard), which first established the doctrine of the one God (his existence, essence, attributes, and operations), and then turned to the triunity of that God (processions, persons, missions)…. A two-part doctrine of God thus preceded the doctrine of creation, at the beginning of the system.
If we move beyond this kind of medieval ‘two-part’ God construct and retrieve constructively from theologians like Athanasius, Epiphanius, et. al. and the ecumenical creeds of Nicea-Constantinople themselves, what we will end up with is a conception of God that understands that God’s oneness and ‘being’ (ousia) is given shape to be what it is by the intra-communion of the threeness of the ‘persons’ (hypostasis), and vice versa. And so we will understand, from the economy or God’s Self-revelation in the Son (see Jn. 1.18), that, as Athanasius has already noted, that to know God, is to know him as the Father of Son, and the Son of the Father, and to know this relationship as given to us by the Holy Spirit come with the Son given for us in the Incarnation. And so we will be left with a statement something like Epiphanius was left with (in the aforementioned).
And yet if the economic revelation (in salvation history) of God as Triune is representative of God in his ontological or immanent life (ad intra), then how do we come to conclude that God is still one, yet three without confusion? How do we affirm that God is ‘simple’ and yet ‘multiplied’ or as Karl Barth says it ‘replicated?’ For brevities’ sake how I understand this question is to posit, along with Scottish theologian, Thomas F. Torrance, that God’s ‘one being’ is mutually shared and given reality (by the interpenetration of the three persons – perichoresis); and so there is a subject-in-being distinction and relation between the persons, such that each person of the Trinity or divine Monarxia can be said to have their distinct roles vis-à-vis the other persons, but that these distinct roles remain inseparably related in their co-inherence one with the other. And so it is this eternal fellowship that the one being of God finds its shape from, while at the same time understanding that this one being is only what it is as the three persons fellowship eternally one with the other; and we know this (pace Athansius) as we look at the Son. As the theologian St. John has written:
7 “If you had known Me, you would have known My Father also; and from now on you know Him and have seen Him.” 8 Philip said to Him, “Lord, show us the Father, and it is sufficient for us.” 9 Jesus said to him, “Have I been with you so long, and yet you have not known Me, Philip? He who has seen Me has seen the Father; so how can you say, ‘Show us the Father’? 10 Do you not believe that I am in the Father, and the Father in Me? The words that I speak to you I do not speak on My own authority; but the Father who dwells in Me does the works. 11 Believe Me that I am in the Father and the Father in Me, or else believe Me for the sake of the works themselves.
There remains then an element of mystery, and yet, it is possible to think God and a grammar for articulating God from his Self-exegesis (see Jn. 1.18) for us as Self-revealed/interpreted in the Son, Jesus Christ.
I would contend then, as I briefly sketched above, that we should avoid the medieval theological practice of attempting to think God as ‘one’ and then as ‘three’, but instead we ought to take our cues from some of the ‘Church Fathers’ (like Athanasius, Epiphanius, et. al.), and some contemporary theologians like Thomas Torrance and Karl Barth, and think of God from the three persons, and understand that ‘there is no God behind the back of Jesus’ as T. F. Torrance was fond of saying in agreement with what the theologian, St. John wrote in the aforementioned passage.
At the end of the day, this becomes a matter of worship as we have been given access to a depth of reality that goes beyond our puny little machinations about what this all means; the good news is that God in his grace has accommodated our weakness, by becoming weak for us (II Cor. 8.9), that we might know and participate in the great riches of his ineffable and Triune life. It seems appropriate then to end this brief essay with a Trinitarian prayer from another famous church Father, St. Augustine.
Should I even ask, O Lord? Should I even ask? You have spoken, and you have acted, and you have called us to believe. You have taught us that we walk by faith and not by sight, by trust in your good promises of goodness, and not by understanding. It is enough that you know the nature of things. Should I ask?
If I ask, will I receive an answer? You are beyond all my thoughts, greater than all that I can say, incomprehensible in your eternal communion as Father, Son, and Holy Spirit. You cannot be encompassed with any concept, bounded by anything greater than yourself, since you are greater than all. All my efforts to encompass you are acts of idolatry and not true worship. And you made all things and all things shine with the bright radiance of your glory. Your world seems as incomprehensible as you yourself.
 Epiphanius, Anc., 10, cited by T. F. Torrance, The Trinitarian Faith, 234-3.
 Athanasius cited by Paul D. Molnar, Thomas F. Torrance: Theologian Of The Trinity, (Ashgate Publishing Limited, England, 2009), 73.
 Fred Sanders, “The Trinity,” in The Oxford Handbook of Systematic Theology, eds. John Webster, Kathryn Tanner, and Iain Torrance (New York: Oxford University Press, 2010), 37.
 See Thomas F. Torrance, Scottish Theology: From John Knox to John McLeod Campbell (Edinburgh: T&T Clark, 1996), 3-4.
 NKJV, John 14:7-11.
 Augustine cited by Peter J. Leithart, Athanasius, xv-xvi.