Having set out his argument from desire in "The Weight of Glory," evoking our longing for our true Home, C.S. Lewis then makes this statement:
Do you think I am trying to weave a spell? Perhaps I am; but remember your fairy tales. Spells are used for breaking enchantments as well as for inducing them. And you and I have need of the strongest spell that can be found to wake us from the evil enchantment of worldliness which has been laid upon us for nearly a hundred years. Almost our whole education has been directed to silencing this shy, persistent, inner voice; almost all our modem philosophies have been devised to convince us that the good of man is to be found on this earth.
Rather than casting the debate as being between faith and reason, Lewis sees the conflict as one of dueling enchantments. Secularism and materialism is an "evil enchantment," and Lewis' argument from desire appeals to romanticism--our deep inner longings and desires--because it is a "spell" he's casting "for breaking enchantments."
The wicked spell of the secular age is the conviction that the deadening materialistic gaze of science is the sole arbiter of "the truth." But that is insanity. The power of science is empirical description, but it's also an acid that strips the world of value and meaning, the magic that make human life human. Lewis' argument from desire may be dinged for being an emotional appeal, a spell he's casting, but at its heart the argument is trying to breath value and meaning back into life. To do this, Lewis evokes fairy tales in a move similar to the one J.R.R. Tolkien makes in his famous essay "On Fairy-Stories." Fairy-stories, says Tolkien, help us recover the world:
Recovery (which includes return and renewal of health) is a re-gaining—regaining of a clear view. I do not say “seeing things as they are” and involve myself with the philosophers, though I might venture to say “seeing things as we are (or were) meant to see them”—as things apart from ourselves. We need, in any case, to clean our windows; so that the things seen clearly may be freed from the drab blur of triteness or familiarity—from possessiveness. Of all faces those of our familiars are the ones both most difficult to play fantastic tricks with, and most difficult really to see with fresh attention, perceiving their likeness and unlikeness: that they are faces, and yet unique faces. This triteness is really the penalty of “appropriation”: the things that are trite, or (in a bad sense) familiar, are the things that we have appropriated, legally or mentally. We say we know them. They have become like the things which once attracted us by their glitter, or their color, or their shape, and we laid hands on them, and then locked them in our hoard, acquired them, and acquiring ceased to look at them.The evil enchantment of science is this possessiveness, this "we say we know them," this acquiring, this mental appropriation which strips the world of value and meaning, of its strange, startling magic. The scientific gaze is like Smaug, it locks the world up in a materialistic box.
The point of the argument from desire isn't an attempt to see things as they are but to "clean the windows" so that we might gaze again at the world the way we were meant to see it.