My friend is not alone. Part of what distinguishes the Narnia series is that it can be read on so many different levels. Setting aside any religious interpretation, it's still just a heck of a good tale.
Nonetheless, a deeply Christian vision shapes Narnia. The most unmistakably Christian trope in "The Lion, the Witch and the Wardrobe"-- Lewis's famous novel about four British children who find themselves in a magical land called Narnia where they meet witches and fauns and a wonderful lion called Aslan--is Aslan's death and resurrection. In order to save one of the children from death at the hands of the evil White Witch, Aslan allows himself to be killed upon a great Stone Table. The "crucifiers" mock him, just as Jesus was mocked: "Why, he's only a great cat after all!"; "Poor Puss! Poor Pussy.... How many mice have you caught today, Cat?" These jeers, of course, recall the soldiers' cry to Jesus: If you are king of the Jews, save yourself!
The resurrected Aslan then reappears to Lucy and Susan. The girls, of course, are taken aback--Susan fears that she is seeing a ghost. But Lucy realizes this is no specter: "Oh, you're real, you're real! Oh, Aslan!" she cries. And Aslan explains that while the White Witch's magic is powerful, there is a deeper, truer, more powerful magic at work--and now that an innocent and willing victim was killed in the intended victim's place, "Death itself would start working backward."
That phrase is about as concise a summary of the Gospel message as one could hope for. Yet the story of Aslan is so engrossing in itself that readers understandably don't always make the connection. Pauline Baynes, who illustrated the first edition of The Chronicles, says she wept while creating the illustration for this scene--but she didn't realize until later that Aslan's death mirrored Christ's suffering on the cross.
The entire Chronicles follow biblical contours. If in "The Lion, the Witch, and the Wardrobe" we have a retelling of Christ's suffering, death, and resurrection, the subsequent Narnia stories tell about the children's adventures in Narnia--their adventures, that is, during the time between Aslan's redemption of Narnia, and his final victory. This is, from the Christian viewpoint, the very same in-between time in which we are living now.
That final coming is reckoned in "The Last Battle," the last book of the Chronicles, which describes the ultimate battle between good and evil, and the final triumph of Aslan. As David Downing has pointed out in his marvelous study "Into the Wardrobe," the very opening of the book sets an apocalyptic tone: "On the last days of Narnia." Echoing the foretelling of the end-times in The Gospel of Matthew and the Book of Revelation, "The Last Battle" depicts the children dying in London and being received at a fabulous banquet by Aslan. Lewis's depiction of Aslan's folding all of history and culture into his kingdom never fails to give me chills:
The things that began to happen...were so great and beautiful that I cannot write them. And for us this is the end of all the stories, and we can most truly say that they all lived happily ever after. But for them it was only the beginning of the real story. All their life in this world and all their adventures in Narnia had only been the cover and the title page: now at last they were beginning Chapter One of the Great Story, which no one on earth has read: which goes on forever: in which every chapter is better than the one before.