What is God like? And how can we find out? He is not part of the universe, so He is not open to scientific investigation. He can’t be dissected, put under a microscope, or analysed by a spectrometer. Can we determine His nature by reason alone, from first principles? Many philosophers, both Christian and non-Christian, have tried. What sort of God do they end up with? Nothing so complicated or uncomfortable as the Christian doctrine of the Trinity. So where does it come from? Straightforward monotheism (‘One God’) would be so much simpler, so much more aesthetically pleasing. It would link Christianity with the god of the Greek philosophers (from Aristotle onward), and with the god of Islam. But it just does not fit with what the Bible tells us about God. And it is the Bible that must be the foundation for all Christian belief.
The word ‘Trinity’ is not found in the Bible (it was coined by Tertullian, around the beginning of the third century). There is nothing particularly unusual about this; you won’t find words such as ‘sacrament’ or ‘monotheism’ in the Bible either. They are useful technical terms, nothing more. And the doctrine of the Trinity is not explicit in the Bible. The Bible is not a theological textbook: it presents us with the facts, and generally leaves us to work out the theology for ourselves. And this is what the early Christians did. The Trinity is not the product of a few mystics huddled together inventing a religion sometime in the fourth century, but the result of three centuries of extended (and sometimes intense) debate as Christians tried to make coherent sense of the data presented to them: the doings and teachings of Jesus of Nazareth, and the experiences of His first disciples and subsequent generations of believers. They especially needed to reconcile the strict Jewish monotheism of Jesus’ first disciples with their deepening convictions about who Jesus was. The end result is “a human endeavour to fit the revelation of God within the limitations of [human] reason.” (Leonardo Boff) It probably isn’t perfect; but it’s the best ‘working hypothesis’ that makes sense of all the Biblical data.
So the word ‘Trinity’ sums up the totality of what the Bible teaches us about the nature of God. The Athanasian creed (probably composed in the fifth century) is the Church’s final, definitive statement on the subject:
“And the catholic faith is this: That we worship one God in Trinity, and Trinity in Unity; neither confounding the persons nor dividing the substance. For there is one person of the Father, another of the Son, and another of the Holy Spirit. But the Godhead of the Father, of the Son, and of the Holy Spirit is all one, the glory equal, the majesty coeternal…”
It’s easy to be put off by the vocabulary: ‘substance’ has a material sound to it, as if God were a lump of rock or plastic, but the actual meaning is more like ‘essence’. The idea that God consists of some kind of ‘single divine substance’ comes from the Greek philosopher Aristotle, and it has become deep-rooted in our thinking because the early Church fathers used his terminology when formulating the creeds. But our God is not ‘a divine substance’; He is spirit (John 4:24), and He is personal. In the Bible, nobody ever meets a ‘divine substance’ – they meet the Father, the Son or the Holy Spirit.
Also, the word ‘person’ does not imply that Father, Son and Spirit are separate individuals – three gods who happened to meet up and now like to hang around together. It means that, although one God (they always act as one and cannot be divided), they can be distinguished from one another – not by any differences in their essential nature, but in the way in which they relate to one another. They are neither identical nor interchangeable, but perform different roles with respect to one another and with respect to us. Even their names make no sense without these distinctions: the Father must have a Son (to be ‘Father’ of), the Son must have a Father (to be ‘the Son’ of), and the Spirit must be ‘the Spirit of’ Someone. And we find as we read the New Testament that the Father sends the Son (never the other way round), the Son obeys the Father (never the other way round), and the Spirit is ‘breathed’ by both Father and Son.
So what exactly do orthodox Christians believe?
That God is one (so we do not worship three separate gods, like the Mormons).
That this one God exists as three distinct ‘Persons’ within that unity (so we are not modalists – who believe that the one God merely manifests Himself in three different ways at different times).
And that all three ‘Persons’ are equally divine (so we are not Arians, like the Jehovah’s Witnesses – who believe that Jesus is a created being, and that the Holy Spirit is an impersonal force).