The Narnia series by C. S. Lewis is one of the greatest contributions to children's literature ever made. The series consists of a number of adventures experienced by a group of children when they are drawn into another world. A portion of this world is named Narnia. Narnia (and the world within it lies) is ruled by a talking lion named Aslan; for much of Narnian history, Narnia proper is under the rule of a witch known as the White Queen, and at other times it is ruled by human kings (born in our world, or descended from persons who were) under the authority of Aslan. The series, in order of publication, ran as follows:
After completing the series, Lewis numbered the books in a different order, to match the internal chronology of the series, and made it his suggestion that the series be read in that order. The result is this:
Personally, I like to read series literature in the order of conception (where possible), or of publication.
The Symbolism
While many younger people read the series and see only the adventures of several children in a magical land ruled by a magical talking lion, adults having any knowledge of Christianity are struck by the allegories to Christian ideas. While many take this as a scheme by C.S. Lewis to peddle Christianity to children, this conclusion must be rejected by the very fact that the alleged target audience rarely if ever recognizes the connection between the two. At the very most Lewis was probably interested in familiarizing the reader with certain ideas.
Hence there are allegories to Biblical themes in the work. Some of it is very overt—the slaughter and resurrection of Aslan is a chief example of this—but some of it is more subtle, such as the restoration of Eustace's human form. For some of the books—The Silver Chair, Prince Caspian, and The Horse and His Boy—there simply aren't any such allegories, and the books that do contain them have them only in parts. To draw upon an analogy made about another body of work, Narnia is not the Bible with the serial numbers filed off. The allegories are there to illustrate, not prove.
It goes without saying that if the symbolism bothers you, your mind urgently requires broadening. If you think that the symbolism constitutes brainwashing, then you really need to (a) learn what brainwashing really means, and (b) figure out the real reason any talk of Christian ideas bothers you.
The Theology
There are quite a few theological points that C. S. Lewis makes in the series.
The obvious point is that just as Aslan is constantly working behind the scenes to bring about his ends, so too does God intervene in a million non-miraculous ways; my own opinion is that God is trying to maximize the number of people who are fit to dwell with Him in eternity, and He is causing things to happen today in order to bring about ends taking place tomorrow, next year, and a thousand years from now.
A major one, accepted by all but a few fringe sects, is illustrated in The Magician's Nephew. When Diggory, Polly, and the rest enter into Narnia for the first time, they find it a void, and a voice—later revealed to be Aslan—sings the new world into existence. Since Aslan represents Jesus Christ—or to be more precise, Aslan is the form that Jesus takes in Narnia—this is Lewis' affirmation that the Son of God did the work of creation in our world as well.
Another point, agreed to by most Christians, is that for salvation we must rely on the Son of God, and not our own efforts, and this is symbolized by Eustace's transformation back into human form: His attempts to remove the dragon skin are painless, but ineffective, as they reveal yet another dragon skin beneath, whereas Aslan's work painfully but effectively removes the whole dragonish nature.
Lewis also properly handles the false dichotomy between salvation by faith and salvation by works: At many places in the series the characters are commanded by Aslan to do something that Aslan could just as easily have done himself. That Diggory brings the apple from Aslan's garden, instead of Aslan fetching it, in no way diminishes the fact that it is Aslan who provides the tree which grows from the apple. In the same way, the fact that certain acts are required of us for salvation does not detract from the necessity of faith, nor does it diminish Christ's role in salvation. "Salvation by faith only" has been taught and accepted in most denominations, even though the phrase faith only appears only in the verse that most strongly denies the doctrine of salvation by faith only (James 2:24).
Lewis' answer to one problem, namely, the fate of those who have never heard the gospel of Christ, or who have been raised hearing nothing but ill about Christ, is illustrated in The Last Battle. In the last book of the series, the children, having entered into paradise, encounter a Calormene (and former enemy). The Calormene relates that although he had served the god Tash all his life, and had believed that Aslan was a demon of some sort, Aslan greets him in paradise with these words: "Son, thou art welcome." It is then explained that because the Calormene had believed in Tash in good faith, and had held himself to noble standards of behavior for Tash's sake, he consequently had been worshipping Aslan all along. Lewis is setting forth a Spiritual Equivalency Principle: If the result is the same, the cause is the same. The implications for the aboriginal who dwells in the Amazonian rain forest and has never heard of Jesus are plain: That there is a general obligation, applicable to all people, to consider one's character and repent of wrongdoing, and there is a specific obligation that applies only to those who have heard of Jesus.
It's fairly obvious that the Calormene's beliefs were obtained from persons whose integrity he had no reason to doubt, and that his beliefs were not employed to rationalize his own whims.
What this all means for Muslims and Jews is a knottier problem; although many Jews and Muslims have the appearance of piety, for some it is merely the appearance. The Calormene was ashamed of the ignoble things he was commanded to do in Tash's name, whereas many Muslims consider any means suitable towards the spread of Islam, and rationalize away any conflicts between the Quran and the desired course of behavior (and they have no lesser person than Mohammed himself as an example to follow in this regard). Additionally, a passage in Hebrews suggests that having heard the gospel makes one subject to the gospel, and since denial of the gospel is taught in both Islam and Judaism (the former denies the crucifixion; both deny Jesus' divinity), both the Muslim and the Jew are responsible to the gospel.
It could be argued that the episode is intended to parallel the career of the apostle Paul, who at first was honestly persuaded that Jesus was not the Christ, and concluded that Jesus' followers were destroying the faith of Abraham; when corrected in his honest mistake, he ceased to be mistaken.
Perhaps the most interesting point is made without anyone remarking on it. In The Last Battle, Good appears to lose to Evil. King Rilian and his meager forces go down fighting, and find themselves in paradise. It then transpires that Aslan intended for Narnia—and the world in which Narnia lies—to come to an end at that point, and that the battle is merely part of His plan for the unmaking of that world.
The Narnia Movies
The original story of the first book fell victim to Producer's Ego. Producer's Ego is when, while a film based on a book is being filmed, the producer changes things for no apparent reason other than his ability to do so; often the excuse is made that it was needful to dramatize something that otherwise would have been uninteresting, but this excuse is too thin in many cases.
Over and over again the producers insert drama where drama had previously not been, for no apparent reason but to make the film more interesting to people who aren't smart enough to appreciate the subtleties of the original tale.
Probably the worst change is the whole entire waterfall scene in the movie; the whole event was producer's fancy and has no basis in the book. It is also where movie-Susan and movie-Peter are at their most annoying. It was added to create drama where no drama had previously existed. If you simply skip the scene, you won't miss a single thing of importance.
Another change, made for the benefit of non-thinking people, was the inflation of the battle scene. This actually made for a set of baffling discontinuities, for between shots of the battle (which takes place entirely in broad daylight), there are interspersed shots of Susan and Lucy at stone table, which are set prior to the dawn, so that we are flipping back and forth in time as well as between two locations. The original flow of the narrative was just fine. It would have been perfectly easy for the entirety of the Stone Table scene to be shown and done; then, after Aslan has departed with Lucy and Susan on his back, we can see the battle begin, the situation become dire, and then finally Aslan show up and put paid to the witch.
And of course when one adds things, those things have to make sense. At the start of the battle, a large number of flying allies drop rocks on the Witch's army. Didn't anyone have the sense to have those birdies concentrate their attack on the Witch? There should have been some explanation of why this wasn't tried or didn't work.
And while the producers were inserting stuff that wasn't there, they left out some rather important things which were in the book. For instance, there was zero effort to get into Edmund's head during the time when he was thinking of betraying his brother and sisters. Surely there was a way to show that the ideas of being made a King by the Witch, and of getting more Turkish Delight, were weighing heavily on his mind. It would show that in traipsing across the snow to the Witch's castle, he was yielding to a strong temptation, instead of simply being an idiot.
Prince Caspian fell victim to Producer's Ego as well. Much of the action in the second film has no basis in the book at all, and a lot of it (Peter and Caspian arguing) directly contradicts the book (wherein they get along without any conflict).
The Future of Narnia
Some of the holders of C. S. Lewis' intellectual property have sent up suggestions that more Narnia material—not written by Lewis—will be forthcoming. While more Narnia would indeed be welcome, there are hints that there will be an effort to avoid the Christian allegories. To me, Aslan isn't Aslan unless he is Narnia's Son of God, and any Narnia without such a person simply isn't Narnia. There remains also the problem of whether the writing will be up to snuff...