“THE Father is God; the Son is God; and the Holy Ghost is God. And yet they are not three Gods; but one God.” So runs the Athanasian Creed.
As far as we know, the word “Trinity” comes from Tertullian (c.155-c.240), who invented its Latin precursor — trinitas — to emphasise that God is threefold (trinus). That, however, is only half of what Christians confess with the doctrine of the Trinity. To revert to the creed of St Athanasius: “We worship one God in Trinity, and Trinity in Unity.”
The doctrine of the Trinity has two halves — three, and one — and most sermons on Trinity Sunday tend to focus on the former. Here, I will tackle the theme of God as one, looking at God’s oneness in terms of uniqueness, plenitude, and simplicity. First, that God is one, with a uniqueness that transcends every category; next, that God is one as a perfect, gathered plenitude; finally, that God is one because everything about God is perfectly unified. Since notions of divine unity might seem rather abstract, for each point I will suggest some consequence for the spiritual or devotional life.
FIRST, then, God is unique. “I believe in one God,” we say in the creeds; but by that we do not mean that there just happens to be only one God — like saying that there is a single pound coin in my pocket, although there could be more, or none at all. We mean something far more profound: there is one God, and God could not be missing or multiplied.
Theologians have found various ways in which to talk about why there could be only one God: because God is the absolute beginning of all other things, for instance; or because God is infinite. In the middle of the 13th century, St Thomas Aquinas pinpointed this when he wrote that God was not one of any wider kind, nor an example of any wider class. God, as he put it, belongs in no genus or species.
That rarefied idea is tremendously important for how we think about God. To say that “God is one” is to say that God is the God, not a god; the God we worship is not an example of some generic kind. This is the antithesis of what I think of as the boring, A-level, god-of-the-divine attributes, which tell us that God is omnipotent, omniscient, omnibenevolent. True enough . . . but we must go further.
Stick with those dull A-level attributes, and we are talking about God as only one example of a general kind: about a god that we have taken down from a shelf of common-or-garden gods. Instead, the one God — the God who lies beyond and before all categories (even the category “god”) — is not a god, but the God, whom we know truly only because God is revealed to us. And, of course, the most striking thing about what God shows us is that this one God is Father, Son, and Holy Spirit. So, for God to be one is for God to be beyond any generic category.
MY SECOND idea is that to call God one is to call God full, perfect, and replete. There is a beautiful passage in Ecclesiasticus 43 in which the author praises God’s wonders in creation, but eventually comes to a halt: “We could say more but could never say enough; let the final word be: ‘He is the all’” (to pan estin autos).
Theologians have again approached the idea that God’s oneness is fullness — “He is the all” — in a variety of ways. We might say that God’s oneness is like the oneness of the sun’s light: a single colour that contains all colours in itself. Or we might say that God’s oneness is infinitude; or that God is one, just as the number one is the root and source of all numbers.
God’s oneness is perfect repleteness; and creation, in all its riotous diversity, only just begins to bear witness to the fullness of its source. This suggests a spiritual exercise for everyday life. As we walk through the city, as we walk through the countryside, as we interact with friends and colleagues, we can seek to see that all their marvellous diversity shows creation making an approximation to the absolutely overflowing boundlessness of the divine one.
So, theologians have said that God is one in a uniqueness that transcends every category, and that God is one as infinite, perfect, gathered plenitude.
FINALLY (at least for this article), God is one in the sense that God is simple.
Close to the heart of the historical Christian doctrine of God as one is the idea that the divine nature transcends division. God is not an amalgam of parts, as we are: everything about God is perfectly gathered, harmonious, and at peace. This theologians have called simplicity, and it is a matter of broad, historically shared theological consensus down the ages. In the Book of Common Prayer, the very first of the Thirty-Nine Articles of Religion lays it out explicitly: there is one God, without “parts or passions”.
Divine simplicity teaches that God is as profoundly one as we can imagine — and, indeed, even more so, since it is to a large part the exceeding oneness of God which puts God beyond all thought. God is one, and all in God is one.
As an example, consider that, for us, to be just is one thing, and to be merciful is another. In God, however, they coincide: God’s mercy is justice and God’s justice is mercy. Similarly, everything in God is perfectly coincident with God’s love. And, while the fact that I am is fundamentally different from what I am, these, too, overlap in God: it is God’s very nature to be. God is simple.
LET me suggest a couple of consequences of this for the spiritual life. We are creatures, and always will be; we are complex, and multiple, and that is how creatures are. We can live at ease with it. We know through a plurality of partial insights, and that is fine. Our knowledge of God does not measure up to God, but it is a marvellous gift, all the same.
Even if our knowledge cannot grasp divine simplicity, however, the more we advance towards God, or are drawn to God, the more we grow into God’s likeness. As we grow into that divine likeness, our mercy becomes more just, and our justice more merciful; and all that we do becomes more of a piece with love.
We may not comprehend divine simplicity with our minds, but we can see it reflected in holy lives. There is an integration to a holy person which mirrors that dimension of the perfect unity of God.
GOD is unique, full, and simple. God is unique, and revealed, not guessed at; God is full, and plenitudinous; and the variety of creation bears witness to that aspect of God as one; God is simple, and we are integrated as people as we grow in God’s likeness.
And, yes, God is also three — but that is not the only thing to think about on Trinity Sunday.
Canon Andrew Davison is Starbridge Lecturer in Theology and Natural Sciences at the University of Cambridge, Fellow and Dean of Chapel at Corpus Christi College, Cambridge, and Canon Philosopher of St Albans Cathedral.