Many people would be surprised if I said that one of the most important questions in the world today is whether there is a God and what God is like. For such people, God has become irrelevant, and practical problems of world hunger, injustice, and ecological disaster are obviously much more important. Those problems are very important, of course. Yet if there is a God, that may be literally of eternal importance. Thinking about God does not in any way prevent trying to tackle practical problems such as that of world hunger – it ought to reinforce efforts to resolve such problems – but it does add another important question to the list of things that are worthy of consideration.

Suppose God is an objective reality of supreme beauty, wisdom, and goodness, and that God has a purpose for the universe, which is, in part, that humans should find their greatest happiness and fulfilment in knowing and cooperating with that supreme goodness. That would make a huge difference to human life. It would give every human life an overriding purpose, meaning, and value, as well as a real hope of achieving a truly worthwhile fulfilment.

I have written this book in the belief that there is such a God. I have written it in a context in which many people have dismissed the idea of God as somehow incoherent or even objectionable. Further, I am a Christian who believes that God is a Trinity, ‘three persons in one substance’, as the tradition puts it. And this is widely thought to be especially absurd. Three into one won't go! I want to put the case that the idea of the Trinity is a profound and intellectually penetrating idea and that it embodies a spirituality – a way of living in dynamic and life-enhancing relation to transcendent values – that can change human lives for the better.

I am not alone. There has been a lot of discussion about the Trinity among Christian theologians in the past century. Much of it has been concerned with developing a fairly new idea of God as dynamic, relational, responsive, and other-creating.