Once upon a time, there was a man who had an image in his head, of a faun walking through a snowy wood, carrying parcels and with an umbrella held above him. And the man decided one day to write a story about that image, a story centered around some children sent away from London during the Blitz.
The man was C. S. Lewis, and that story was The Lion, the Witch, and the Wardrobe, the first of the Chronicles of Narnia to be written and published.
The seven Narnia books – in internal chronological order The Magician's Nephew; The Lion, the Witch, and the Wardrobe; The Horse and His Boy; Prince Caspian; The Voyage of the Dawn Treader; The Silver Chair; and The Last Battle – were first published in a seven year period from 1950 through 1956 and have been, deservedly, in print continuously since that time. The publication order was significantly different; Lion was published first, followed by Prince Caspian, Dawn Treader, and Silver Chair which all together form a fairly tight continuous arc of mortal boys and girls performing their vital roles for Narnia. Following those, The Horse and His Boy was published as a sort of "interquel" (it happens in the long but very little described period during which the Pevensie children grew up and ruled Narnia, basically in the last few pages of Lion), and then the final two books which covered, appropriately, the Beginning and the End of Narnia, "bookending" the prior novels.
Interestingly, not only did the book series begin with a simple image in Lewis' head, but it took several books before Lewis began to think of it as a series. While it incorporates many Christian themes, it was not – as I have heard some people contend – written as some sort of deliberate Christian story cycle.
Most people are familiar with the basic premise of Lion, at least, and the series in general. Four young British children find themselves transported to a magical land under the oppressive rule of the White Witch, and through various circumstances help free Narnia from the Witch's grasp and are eventually crowned Kings and Queens of Narnia. Other books show the same children, and others, brought into Narnia to help at crucial moments of history. The Magician's Nephew shows how Narnia was first created, and how the White Witch came to be there, and The Last Battle shows the end of that world ("or is it?…"), while The Horse and His Boy gives us a look at life in parts of the world of Narnia that we otherwise did not see, and from the point of view of a native rather than one of the earth-born children (we only have such a viewpoint in one other book, specifically The Last Battle).
EDIT: Actually, we also get one in Prince Caspian.
I encountered Narnia, if I recall correctly, in my early teen years and was immediately charmed by them. Even then I realized this was depicting a society mostly gone and from only one point of view, but to me it was sort of a mythic era in and of itself, somehow connected to all the old English writing of Doyle and Wells and Christie and the magical stories of Nesbit and Eager.
One thing I did not realize when reading them was the Christian elements. To me, the (obvious now) parallels between Christ's crucifixion and Aslan's self-sacrifice at the Stone Table were lost. That sequence was simply a powerful magical ritual and symbol and a surprising gambit played out by the Lion; I was later puzzled by Aslan's statement in The Voyage of the Dawn Treader that "I have another name in your world,", as I couldn't think of any Lion-gods that fit the description.
If anyone reading this finds that to be unlikely, you should understand that I was raised without any knowledge of active religion in my house; there was neither promotion nor denigration of religion in my household, and I was, in fact, an adult by the time I realized that there really were people who believed in actual gods of various sorts still alive; I had a vague impression that religion as an actuality had died out somewhere after the late 1800s, leaving churches as sort of social meeting places bound by a tradition but no actual belief. It was only many years later that I found out my mother had been raised in a strict Lutheran household; I have, to this day, no idea whatsoever what my father's beliefs were on the subject.
Because of this odd perspective, I was capable of reading and judging the Chronicles of Narnia purely as stories for young people. From an adult view, of course, there's too much arbitrary (and literal) deus ex machina to make the stories entirely satisfying, but from a kid's point of view it makes sense; the children in the books have very specific parts to play, and their courage and decisiveness are important to help develop themselves as well as assist the people in the world around them.
The fact that there are rules, and a powerful force to be brought to bear when things are truly terrible, certainly reflects religion… but it also reflects childhood, in which it's important for children to make decisions, try to solve their problems, and their actions can rebound on themselves and others… but when things become too serious they are supposed to be able to turn to their parents to deal with the consequences. If they've done the overall right things, their parents will support them and take action to protect them and make things right.
In this sense, the Narnia books also provide a preview of growing up – the need to recognize larger consequences and view things in a different way than those of mere children. Eustauce is undoubtedly the poster child for growing up due to Narnia's influence, but all of the children are positively affected by their presence in Narnia and can generally face their home world better for having had their adventures.
It's interesting that Narnia is shown to be able to have the opposite effect than some other children's "portal" fantasies; the children generally remember their adventures in Narnia long after they return, even if they physically are returned to the same condition they had when they left. If they stay too long, in fact, their memory of our world begins to fade, as shown by Edmund, Peter, Lucy, and Susan when they have ruled Narnia for many years.
Narnia is one of the few series to actually show the Beginning and End of its world; we get to see Narnia's creation – literally being sung into existence by Aslan in The Magician's Nephew, and being shut down into eternal frozen darkness in The Last Battle – and all of this happening in what is, for our world, a matter of 50 years corresponding to over 2500 years of Narnian history.
At first glance this might seem a very sad element of Narnia, as is the fact that once children pass a certain age they are told they can no longer enter Narnia; but in fact Narnia presents what is, to me, the best vision of what "heaven" could be that I have ever seen. For at the end of the Chronicles, we discover that "Aslan's Country", which is where the survivors of the Last Battle find themselves, is Narnia – a greater, better Narnia with more and finer adventures to have, and every day and adventure better and more exciting than the last… forever, with an even greater version of Narnia always waiting to be discovered. This is not an afterlife of boredom, or empty hosannahs, or even a glorious warrior afterlife which wouldn't appeal to anyone not a mead-swilling killing machine. This is a world, just one that's better – and always getting better – version of the world we were born to and made for, one where the old are made young, the crippled can walk, the blind can see, and no joy is too great to be felt. It also connects to all versions of "Aslan's Country" – all worlds, in short – so that one is not only stuck in some great version of Narnia, but can go home to a greater version of Britain, or visit the "true" version of America", or presumably an infinity of other worlds and countries as well.
Lewis' Narnia also makes clear that it is the will and heart and decisions that matter, not whether someone is a follower of a particular name or set of rituals: we encounter in Aslan's Country a Calormene prince who has followed the religion of Tash (generally depicted as something close to, if not actually, demon worship) all his life, but has conducted himself in an honorable, righteous, and decent manner throughout. To him, Aslan explains:
For I and [Tash] are of such different kinds that no service which is vile can be done to me, and none which is not vile can be done to him.Therefore if any man swear by Tash and keep his oath for the oath’s sake, it is by me that he has truly sworn, though he know it not, and it is I who reward him.
And if any man do a cruelty in my name, then, though he says the name Aslan, it is Tash whom he serves and by Tash his deed is accepted.
Because the books are interpreted often in a Christian light, they often come under perhaps more adult scrutiny than many childrens' books, and this certainly applies when we consider "The Question of Susan". At the end of the Chronicles, all of the children we have seen in all the books end up permanently in the "true Narnia", and it is discovered that this is because they have in fact died in the "real world"; a terrible accident on the railway has resulted in their deaths.
With one exception: Susan Pevensie.
Susan is shown to have grown apart from her siblings, and in fact to have actively rejected her memory of Narnia, calling it a "game" they used to play. Other comments include her being too interested in things like "nylons" and "parties" and so on. This is, by various people, depicted as indicating a negative attitude towards someone "growing up", and to an extent this is probably true. Often the sequence is also interpreted to mean that Susan is going to hell, so to speak, and that this is because she has rejected Narnia; in short, if she chooses to live in the adult, material world, she's rejecting the salvation of God/Aslan.
In my view, this is however something of a misperception because this sequence of events reflects Lewis' overall attitude, as shown in the commonly quoted passage:
Critics who treat 'adult' as a term of approval, instead of as a merely descriptive term, cannot be adult themselves. To be concerned about being grown up, to admire the grown up because it is grown up, to blush at the suspicion of being childish; these things are the marks of childhood and adolescence. And in childhood and adolescence they are, in moderation, healthy symptoms. Young things ought to want to grow. But to carry on into middle life or even into early manhood this concern about being adult is a mark of really arrested development. When I was ten, I read fairy tales in secret and would have been ashamed if I had been found doing so. Now that I am fifty I read them openly. When I became a man I put away childish things, including the fear of childishness and the desire to be very grown up.
Susan is not in True-Narnia with them for two reasons: first, and most important, is that she is not dead yet. The time ratio between our world and that of Narnia has always been very large, and she was not on that train, so quite considerable time may elapse before she does die.
Second, she has at that point chosen to forget the lessons learned in Narnia, or at least reject any contemplation of that set of events because it does not fit with the rest of the world she knows. This is, of course, the world of 1940s Britain, with extreme social pressures especially on adolescent and young adult women (by the end of The Last Battle, Susan is only 21 years old). It is utterly unsurprising that peer pressure and the additional pressure of WWII would make it easy, even appealing to "fit in" with the society around her (especially since she has long since known by Aslan's statement that she will never return to Narnia). Peter and Edmund are young men and subject to different pressures, and Lucy is both younger and was always willing to stick by her own views regardless of others, so they are not affected in the same way.
The question then remains as to whether this is a permanent state of affairs; has Susan rejected any chance of rejoining her family in the afterlife, in effect rejecting the salvation of heaven? The events surrounding the Calormene prince, and Lewis' other writings, would indicate that the answer is "no"; firstly, she will be judged for her works and intentions during her life, and minor pettiness is unlikely to damn her. Moreover, salvation is quite possible even at the end; The Screwtape Letters show this very event at the end – despite all the great care and effort devoted to corruption and distraction by the demon "Wormwood", all of that is effectively undone in a matter of instants and his "client", instead of descending to Hell, ascends to the Light.
Susan merely serves as an example of choices – that just seeing Narnia is not enough for salvation, nor is even doing good works in Narnia alone. One could argue that perhaps it should have been Peter or Edmund instead of Susan, but on the other hand Edmund had already performed the role of Judas, effectively, and repented, and would it be fair, so to speak, to cast both boys as somehow more open to corruption and both girls as faithful and loyal?
In truth, though, most of these questions are, to my mind, irrelevant in the larger sense. The importance of the Narnia books is in their reading, in the fact that they provide a world of wonder and beauty and adventure that young readers – and some not-so-young readers – can journey to along with the young protagonists and find themselves part of. I love these books; I've read them to all of my kids as they've become old enough to understand them, and I expect to continue that tradition until all of them are too old for me to read to them.
I salute C.S. Lewis and his inspired creation, sprung from a single mental image.