When you think about it, it’s obvious. Jesus didn’t write books, yet he’s the Author (and Finisher) of our faith. John tells us that Jesus is the Word of God, made flesh and living among us. This is such an important doctrinal Truth and a mystical joining of what was and what is. God speaks creation into existence and Jesus is, “begotten of the Father before all worlds, Light of Light, very God of very God, begotten, not made, being of one substance with the Father”, as the creeds explains. Jesus is God both known and revealed.
Christianity is at once the answer to our deepest longings and riddled with difficulty in our want for concreteness. Lewis addresses this in various places, in Mere Christianity, Abolition of Man, Miracles, and Surprised by Joy, for example. As it should be, the point is central to Lewis’s faith and his sense of being drawn into faith. At every turn, we hear him talking about Christianity as the myth made complete and shown True, which is part of this same sense of following the Incarnate God-man who is Jesus, and not simply following a truism or an ideal.
Here’s a specific occasion he addresses this in Reflection on the Psalms. I found it helpful and I hope you do as well.
“We might have expected, we may think we should have preferred, an unrefracted light giving us ultimate truth in systematic form — something we could have tabulated and memorized and relied on like the multiplication table. One can respect, and at moments envy, both the Fundamentalist’s view of the Bible and the Roman Catholic’s view of the Church. But there is one argument which we should beware of using for either position: God must have done what is best, this is best, therefore God has done this. For we are mortals and do not know what is best for us, and it is dangerous to prescribe what God must have done — especially when we cannot, for the life of us, see that He has after all done it.
“We may observe that the teaching of Our Lord Himself, in which there is no imperfection, is not given us in that cut-and-dried, foolproof, systematic fashion we might have expected or desired. He wrote no book. We have only reported sayings, most of them uttered in answers to questions, shaped in some degree by their context. And when we have collected them all we cannot reduce them to a system. He preaches but He does not lecture. He used paradox, proverb, exaggeration, parable, irony; even (I mean no irreverence) the ‘wisecrack’. He utters maxims which, like popular proverbs, if rigorously taken, may seem to contradict one another. His teaching therefore cannot be grasped by the intellect alone, cannot be ‘got up’ as if it were a ‘subject’. If we try to do that with it, we shall find Him the most elusive of teachers. He hardly ever gave a straight answer to a straight question. He will not be, in the way we want, ‘pinned down’. The attempt is (again, I mean no irreverence) like trying to bottle a sunbeam.”