What is the doctrine of the Trinity for?

In a recent BHT post, I mentioned that the doctrine of the Trinity was never a barrier to faith for me, but instead one of the key teachings that drew me back to the Christian faith. This was particularly true of C.S. Lewis’s account of the Trinity in Mere Christianity.

Lewis addresses the Trinity in the fourth part of Mere Christianity, and in particular in the chapter “Good Infection”. He begins by describing the eternal relationship between the Father and the Son:

[W]e must think of the Son always, so to speak, streaming forth from the Father, like light from a lamp, or heat from a fire, or thoughts from a mind. He is the self-expression of the Father—what the Father has to say. And there never was a time when He was not saying it.

However, Lewis continues, the problem here is that “these pictures of light or heat are making it sound as if the Father and Son were two things instead of two Persons”. Hence we should always go back to that personal language of Father and Son that we find in the Bible:

Naturally God knows how to describe Himself much better than we know how to describe Him. He knows that Father and Son is more like the relation between the First and Second Persons than anything else we can think of.

Much the most important thing to know is that it is a relation of love. The Father delights in His Son; the Son looks up to His Father.

This is what Christians mean by saying that “God is love”. Not that “love is God” (which is what some end up meaning by the phrase), but that:

…the living, dynamic activity of love has been going on in God for ever and has created everything else.

So this is the first major consequence of the doctrine of the Trinity for us: it gives us a way to say that “God is love” in a meaningful way.

This transforms our understanding of what God is like:

And that, by the way, is perhaps the most important difference between Christianity and all other religions: that in Christianity God is not a static thing—not even a person—but a dynamic, pulsating activity, a life, almost a kind of drama. Almost, if you will not think me irreverent, a kind of dance.

This “kind of dance” is then how we are to understand the Holy Spirit:

The union between the Father and Son is such a live concrete thing that this union itself is also a Person. […] What grows out of the joint life of the Father and Son is a real Person, is in fact the Third of the three Persons who are God.

Lewis suggests that some people may find it easier to start with this third Person, the Holy Spirit, and work backwards:

God is love, and that love works through men—especially through the whole community of Christians. But this spirit of love is, from all eternity, a love going on between the Father and Son.

I hope by now it’s clear that, for Lewis, the Trinity is no dry dogma on the page; not just a set of abstract nouns to be memorised in the right order. Rather, it goes to the heart of what it is to be a Christian, as Lewis sets out in a passage that, with hindsight, converted me to Christianity as I read it – though it took me a month or two to realise:

And now, what does it all matter? It matters more than anything else in the world. The whole dance, or drama, or pattern of this three-Personal life is to be played out in each one of us: or (putting it the other way round) each one of us has got to enter that pattern, take his place in that dance. There is no other way to the happiness for which we were made. Good things as well as bad, you know, are caught by a kind of infection. If you want to get warm you must stand near the fire: if you want to be wet you must get into the water. If you want joy, power, peace, eternal life, you must get close to, or even into, the thing that has them.

They are not a sort of prizes which God could, if He chose, just hand out to anyone. They are a great fountain of energy and beauty spurting up at the very centre of reality. If you are close to it, the spray will wet you: if you are not, you will remain dry. Once a man is united to God, how could he not live forever? Once a man is separated from God, what can he do but wither and die?

I’ll never forget reading that for the first time and thinking, “If I was going to believe in a God, that’s the sort of God I’d want to believe in”.

So that’s what the doctrine of the Trinity means in practice for us as Christians: that we are to share in the life of Christ, united to him:

If we do, we shall then be sharing a life which was begotten, not made, which always has existed and always will exist Christ is the Son of God. If we share in this kind of life we also shall be sons of God. We shall love the Father as He does and the Holy Ghost will arise in us. He came to this world and became a man in order to spread to other men the kind of life He has—by what I call “good infection.”

This is what we are called to be as Christians; this is what Christians are for:

Every Christian is to become a little Christ. The whole purpose of becoming a Christian is simply nothing else.


3 thoughts on “What is the doctrine of the Trinity for?”

  1. Yes. This.

    Thank you for stating it so clearly (and indeed for bringing back to mind the passages in Lewis where he states it so clearly). “Once a man is united to God, how could he not live forever? Once a man is separated from God, what can he do but wither and die?” is perfect.

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