Preachers often dread Trinity Sunday. Why? Because they feel that, though you know where you are when you are preaching about most Christian doctrines, things become impossibly murky when it comes to the Trinity --- that to preach on Trinity Sunday means trying to talk about something one does not understand.
In that case, however, every Christian preaching engagement should be approached in a state of panic. For the whole Christian religion rests on a belief in what we do not understand.
You may think that your powers of thought have broken down when you try to think about the Trinity. But your reason has broken down as soon as you start thinking about God at all. The Trinity is not more mysterious than God since God himself is strictly inconceivable.
By 'God' here I mean the Creator of the universe --- the one who 'calls into existence the things that do not exist' (Rom 4:17). And if God is our Creator, he makes us to be and is the source of all the goodness that we exhibit or encounter.
So belief in God the Creator gives us reason to be grateful. If God the Creator is the cause of all creaturely being and goodness, and if God creates freely and knowingly, then we should doubtless think of him as one to be thanked.
But does this mean that we should also think of him as one who is especially concerned with us?
Considered simply as Creator, God cannot be thought of as more concerned with us than he is with anything else that he makes and does well by. It certainly makes sense to say that God shows love to us by willing what is good for us.
Such love, however, might also be thought of as rather colourless. The love which tends to interest most people goes beyond just a matter of willing what is good. So can the love of God be construed as more than a matter of benevolence? Can we, for instance, truly speak of God as being in love with us?
When we speak of people loving each other we are thinking of a relationship between equals. So God the Creator, considered simply as such, cannot be thought of as being in love with us. There is no natural equality between creatures and God. They are naturally as unequal as it is possible to be.
But what if God has found an equal to love? And what if that equal ends up treating us as his equal? Then, perhaps, we can finally speak of God being in love with us. If God loves another equal to himself, and if we are invited to share in that love, then God stands to us as more than just benevolent.
And yet that is how God stands to us in the light of the doctrine of the Trinity. With the doctrine of the Trinity we at last have reason to say that God is loving in and of himself and not just because he makes good creaturely things. Because of the doctrine of the Trinity we can say that God the Father loves God the Son (his equal) and that the bond between them is God the Holy Spirit (their equal).
And because of the doctrine of the Incarnation we can say that the eternally beloved of the Father has become one of us, that he has called us not his servants but his friends (John 15:15), and that he pours forth on us the Spirit which unites him and his Father.
The Word is brought forth eternally by the Father and is just what the Father is as God (John 1:1). Yet this Word came among us and told us that we are to him as he is to the Father (John 15:9).
Our God is not just a mysterious and kindly Creator. He is a life of love in his own right. And he calls us to share in that. And this, in the end, is why the doctrine of the Trinity matters.
The second letter of Peter tells us that God has called us 'to his own glory and excellence' so that we may become 'partakers of the divine nature' (2 Pet 1:3-4). The claim may seem preposterous. But it is what we believe just because we believe in the triune God who has revealed himself to us in the person of Jesus of Nazareth.
So Christian preachers would do well not to shy away from it or to think of it as something they should panic about as they step into their pulpits.