Child, if you will, it is mythology. It is but truth, not fact: an image, not the very real. But then it is My mythology. The words of Wisdom are also myth and metaphor: but since they do not know themselves for what they are, in them the hidden myth is master, where it should be servant: and it is but of man’s inventing. But this is My inventing, this is the veil under which I have chosen to appear even from the first until now. For this end I made your senses and for this end your imagination, that you might see My face and live. What would you have? Have you not heard among the Pagans the story of Semele? Or was there any age in any land when men did not know that corn and wine were the blood and body of a dying and yet living God? -—The Pilgrim’s Regress 169In the Space Trilogy, as we have seen, Lewis took a pre-Christian mythology and an astrological system and combined them into a work of glorious Christian fiction. In Till We Have Faces, he went one step further: he simply told a myth, without ever breaking into New Testament language or inserting Pauline doctrine or drawing Anglican conclusions. How, then, is Till We Have Faces anything other (or more) than simply a retelling of a Pagan myth?
Well, the simple answer is that Lewis used Psyche’s and Orual’s relations with the god of the mountain as metaphors for true spiritual relations between a Christian’s soul and Christ. But this easy answer doesn't tell the whole story. A fuller interpretation needs to include Lewis’s concept, that Christianity is the one myth that happens to have happened, and that all other myths contain shreds of Christian truth because they are foreshadowing the actual events of Christ’s earthly life (cf. Surprised 62).
After years of studying philosophy, literature, mythology, and religion, Lewis had learned not to ask Which is “the one simply true religion among a thousand religions simply false?” Instead, he asked “Where has religion reached its true maturity? Where, if anywhere, have the hints of all Paganism been fulfilled?” (Surprised 235).
Dyson and Tolkien showed me… that if I met the idea of sacrifice in a Pagan story I didn’t mind it at all… I liked it very much and was mysteriously moved by it… I was prepared to feel the myth as profound and suggestive of meanings beyond my grasp tho’ I could not say in cold prose ‘what it meant.’ Now the story of Christ is simple a true myth…. the Pagan stories are God expressing Himself through the minds of poets … while Christianity is God expressing Himself through what we call ‘real things’” (Green 117).By calling Christianity “The True Myth,” Lewis did not mean to suggest that the details recorded in the Bible, especially the Gospels, did not happen. On the contrary, he believed that “Myth does not equal the non-historical; myth equals the non-describable. The outline of the mythological story is analogous to the metaphor in poetry. …The distinction of mythology and history must be a result of The Fall” (Carnell 124-5; cf. Perelandra 45, emphasis mine). Lewis insisted that there had been an historical person named Jesus; that He did live and teach and speak the words the Gospels record; that He did perform miracles, die, and rise from the dead bodily; and that His death was efficacious for salvation—-in short, all those essential points of the Creeds. But Lewis also thought that the whole Gospel story had the emotional and imaginative power of a myth: a God comes to earth, dies, is reborn in the Spring.
The following passage from the letters explains more of Lewis’s ideas about mythology and truth.
Anyway, if you take the sacrificial idea out of Christianity you deprive both Judaism and Paganism of all significance. Can one believe that there was just nothing in that persistent motif of blood, death, and resurrection, which runs like a black and scarlet cord through all the greater myths—thro’ Balder & Dionysus & Adonis & the Graal too? Surely the history of the human mind hangs together better if you supposed that all this was the first shadowy approach of something whose reality came with Christ—even if we can’t at present fully understand that something (II:35).Thus Lewis, the mature Christian who led a generation back to the Bible through his BBC broadcast talks and held an honorary doctorate in Theology was able to write with absolute comfort inside an entirely pre-Christian, Pagan world. Till We Have Faces was the scaffolding whereby Lewis was able to give images of kingship, birth, love, sacrifice, ritual marriage, loss, despair, wandering, blood, death, resurrection, and visionary ecstasy.