This has been making the rounds for some time, but it is great fun for theology geeks and worth sharing again on this Trinity Sunday!
St. Augustine on the Mystery of God
What then, brethren, shall we say of God? For if you have been able to comprehend what you would say, it is not God; if you have been able to comprehend it, you have comprehended something else instead of God. If you have been able to comprehend Him as you think, by so thinking you have deceived yourself. This then is not God, if you have comprehended it; but if it be God, you have not comprehended it. How therefore would you speak of that which you can not comprehend?
– St. Augustine of Hippo
C. S. Lewis on the Trinity and Prayer
You may ask, “if we cannot imagine a three-personal Being, what is the good of talking about Him?” Well, there isn’t any good talking about Him. The thing that matters is being actually drawn into that three-personal life, and that may begin any time – tonight, if you like. What I mean is this. An ordinary simple Christian kneels down to say his prayers. He is trying to get into touch with God. But if a Christian, he knows that what is prompting him to pray is also God: God, so to speak, inside him. But he also knows that all his real knowledge of God comes through Christ, the Man who was God – that Christ is standing beside him, helping him to pray, praying for him. You see what is happening. God is the thing to which he is praying – the goal he is trying to reach. God is also the thing inside him which is pushing him on – the motive power. God is also the road or bridge along which he is being pushed to that goal. So that the whole three-fold life of the three personal being is actually going on in that ordinary little bedroom where an ordinary Christian is saying his prayers.
C.S. Lewis, Mere Christianity, 143