I have two thoughts. First, the main argument Lewis makes in his preface (which you’ll just have to read – it’s not too long) reminds me of something he says at the end of The Abolition of Man. Not the exact same issue, but the same method is in question from a different angle.

You cannot go on ‘seeing through’ things forever. The whole point of seeing through something is to see something through it. It is good that a window should be transparent, because the street or the garden beyond is opaque. How if you saw through the garden too? It is no use trying to ‘see through’ first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To ‘see through’ all things is the same as not to see.

Second, I very much like the last passage of Lewis’s preface, where he says how certain books can be quite satisfying even if you disagree with them.

It has also given me that bracing and satifying experience which, in certain books of theory, seems to be partially independent of our final agreement or disagreement. It is an experience most easily disengaged by remembering what has happened to us whenever we turned from the inferior exponents of a system, even a system we reject, to its great doctors. I have had it on turning from common “Existentialists” to M. Sartre himself, from Calvinists to the Institutio, from “Transcendentalists” to Emerson, from books about “Renaissance Platonism” to Ficino. One may still disagree (I disagree heartily with all the authors I have just named) but one now sees for the first time why anyone ever did agree. One has breathed a new air, become free of a new country. It may be a country you cannot live in, but you now know why the natives love it. You will henceforward see all systems a little differently because you have been inside that one. From this point of view philosophies have some of the same qualities as works of art. I am not referring at all to the literary art with which they may or may not be expressed. It is the ipseitas, the peculiar unity of effect produced by a special balancing and patterning of thought and classes of thoughts: a delight very like that which would be given by Hesse’s Glasperlenspiel (in the book of that name) if it could really exist. I owe a new experience of that kind to Mr. Harding.

This is something I look for when I read books of different persuasions than my own. I think the experience is rare.