In short, The Lion, the Witch, and the Wardrobe by C.S. Lewis presents a Christian worldview through a mythic tale. It takes place in Narnia, a world of magic. In Narnia, virtually every fairy tale or mythic creature imaginable comes alive. But unlike much fantasy, such as the realm of Harry Potter, Narnia is another world—a separate creation from ours. In Narnia, what we would call "magic" is simply part of the created order (the wardrobe is actually from Narnia too, although this is known from a previous story). Thus, the mythic elements are used as a vehicle to tell a bigger story, not to promote falsehood in the real world.
The Lion, the Witch, and the Wardrobe is an allegory, and in an allegory it is important to understand what the symbols are referring to. For example, Aslan’s death and coming to life is a portrayal of Christ’s substitutionary atonement. It does not matter that it was not on a cross or that some elements are separated or out of order in time from the biblical gospel story. What matters is that the picture is correct – and it is. Aslan (Christ) has willingly humiliated himself and died for the sons of Adam (specifically Edmund) whom sin and death (the White Witch) have a right to take due to the “deep magic” (the Law) of Narnia. But Aslan rises again (resurrection), accompanied by an earthquake and discovered by two girls (the two Marys). His resurrection destroys the power of the deep magic over mankind (nailing our sins to the cross). Aslan then goes on to breathe life into his warriors (the Holy Spirit coming on all disciples) so that they may wage war with him against the White Witch and her armies (spiritual warfare). Aslan ultimately wins, bringing in a re-created world (new heavens and earth).
The Lion, the Witch, and the Wardrobe also presents a biblical portrait of Christ in the character of Aslan. Some have complained that as a Christ-figure Aslan should not have taken part in the killing of the White Witch. But the book of Revelation says that Christ will indeed destroy evil at His return—and it will not be pretty. The politically correct/humanistic/liberal community is simply not used to thinking of evil as something to be fought, and that such fighting is not only right, it is valorous. The Lion, the Witch, and the Wardrobe reminds us of this truth.
There are many other gems in this story. A stirring, single-line description of God comes at the point when the children are in Beaver’s dam. Lucy asks Beaver if Aslan is safe, and Beaver replies, "Safe? Of course he isn’t safe! . . . But he’s good." Another classic line comes when Lucy’s siblings approach their uncle about Lucy’s bizarre belief in Narnia. After they admit that she has never been known to lie and does not appear to be insane, their uncle then replies that, logically, she should be believed! This is Lewis’ famous “trilemma”—where Christ’s claims to divinity are shown to be believable due to the absurdity of the other explanations.
All in all, The Lion, the Witch, and the Wardrobe presents the gospel in a powerful way that children can relate to, and adults can still learn from.