C.S. Lewis writes, "Many people nowadays say, 'I believe in a God, but not in a personal God.' They feel that the mysterious something which is behind all other things must be more than a person. Now the Christians quite agree. But the Christians are the only people who offer any idea of what a being that is beyond personality could be like. All the other people, though they say that God is beyond personality, really think of Him as something impersonal: that is, as something less than personal. If you are looking for something super-personal, something more than a person, then it is not a question of choosing between the Christian idea and the other ideas. The Christian idea is the only one on the market."
"Some people think that after this life, or perhaps after several lives, human souls will be 'absorbed' into God.... They say it is like a drop of water slipping into the sea. But of course that is the end of the drop.... It is only the Christians who have any idea of how human souls can be taken into the life of God and yet remain themselves—in fact, be very much more themselves than they were before. I warned you that Theology is practical. The whole purpose for which we exist is to be thus taken into the life of God."
"A world of one dimension would be a straight line. In a two-dimensional world, you still get straight lines, but many lines make one figure. In a three-dimensional world, you still get figures but many figures make one solid body.... As you advance to more ... complicated levels, you do not leave behind ... the things you found on the simpler levels: you still have them, but combined in new ways—in ways you could not imagine if you knew only the simpler levels.... The Christian account of God involves just the same principle.... On the human level one person is one being, and any two persons are two separate beings.... On the divine level you still find personalities; but ... combined in new ways.... In God's dimension ... you find a being who is three Persons while remaining one Being, just as a cube is six squares while remaining one cube.... We cannot fully conceive a Being like that: just as, if we ... perceived only two dimensions ... we could [not] properly imagine a cube. But we can get a sort of faint notion of it. And when we do, we are then ... getting some positive idea ... of something super-personal—something more than a person."
"The thing that matters is being actually drawn into that three-personal life, and that may begin anytime.... 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 ... 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 [God-Man] beside him, helping him to pray, praying for him. God is the [Person] to [whom] he is praying—the goal he is trying to reach. God is also the [Person] inside him [who] is pushing him on—the motive power. God is also the road or bridge along which he is being pushed to that goal.... The whole three-fold life of the three-personal Being is actually going on ... [when] an ordinary man is saying his prayers. The man is being caught up into ... Zoe or spiritual life: he is being pulled into God, by God, while still remaining himself."
"That is how [trinitarian] Theology started. People already knew about God in a [somewhat] vague way. Then came a man who claimed to be God; and yet He was not the sort of man you could dismiss as a lunatic. He made them believe Him [that Jesus is fully God and fully man]. They met Him again after they had seen Him killed. And then, after they had been formed into a little ... community, they found God somehow inside them as well: directing them, making them able to do things they could not do before. And when they worked it all out they found they had arrived at the Christian definition of the three-personal God. This definition is not something we have made up." Trinitarian theology is NOT 1 + 1 + 1 = 3 but 1 x 1 x1 = 1.
"Theology is, in a sense, an experimental science. It is simple religions that are the made-up ones.... While in other sciences the instruments you use are things external to yourself (things like microscopes and telescopes), the instrument through which you see God is your whole self. And if a man's self is not kept clean and bright, his glimpse of God will be blurred—like the moon seen through a dirty telescope.... The one really adequate instrument for learning about God is the whole Christian community, waiting for Him together. Christian brotherhood ... is the technical equipment for this science—the laboratory outfit. That is why ... people who turn up every few years with some ... religion of their own as a substitute for the Christian tradition are really wasting time. Like a man who has no instrument but an old pair of field glasses, setting out to put all the real astronomers right. He may be a clever chap—he may be cleverer than some of the real astronomers, but he is not giving himself a chance. And two years later everyone has forgotten all about him, but the real science is still going on. If Christianity was something we were making up, of course we could make it easier. But it is not. We cannot compete, in simplicity, with people who are inventing religions. How could we? We are dealing with Fact. Of course anyone can be simple if he has no facts to bother about."
Highlights from Chapter 2: The Three-Personal God from Book 4: Beyond Personality, or First Steps in the Doctrine of the Trinity in Mere Christianity by C.S. Lewis. Click here for a clear view of how this chapter relates to the whole book.