I guess my initial thought, without having looked at it, is that it scarcely makes sense to do a Bible study based on the Chronicles of Narnia when there are 66 books in the Protestant canon that are much worthier of study, and that actually are the canon, rather than one man's children's version of a relatively small segment, mixed in with his own understanding of doctrine.
There is an appalling amount of biblical illteracy in the American church, particularly among evangelicals who claim that the Bible is the basis for their faith. The best way to correct that is to read the Bible, not the Chronicles of Narnia.
It's also interesting to note that almost every sermon and particularly every online Christian article C. S. Lewis is quoted, like he is the only person that has ever written about Christ. It's ironic, because in the introduction to "Mere Christianity," C.S. Lewis himself wrote about that very problem.
More seriously, I think it's due to a few factors:
- Lewis is more contemporary and accessible than many of the great Christian apologists from years past, and although he was an Oxford don, he wrote for the common masses.
- Many of us who are now adults and leaders in some capacity within the church were raised on Narnia, and as we grew, we find more Lewis books waiting for us, from "The Great Divorce" to "Mere Christianity" and "The Problem of Pain." The guy wrote a lot.
- As I said, we're an illiterate bunch, especially when it comes to the Bible. It's an ancient document, and it doesn't fit our pleasant little doctrines nearly as much as we pretend it does, so it's easier to read a book by J.I. Packer, R.C. Sproul, or C.S. Lewis, and then feel that we understand the faith. (Which we might, after a fashion, but not as well nor as purely as if we took the time to study the Scriptures themselves for us.)
- Lewis wrote at a time when the British church was at a similar point to where the American church now finds itself. People were no longer taking the church as an authority morally or spiritually, and were leaving in droves. Society was moving from primarily Christian to primarily post-Christian. Thus, his writing as a Christian in that context speaks to us in ours.
Mind that I'm deliberately taking an overstrident position just to provoke the discussion, but in basing the study on another book -- another story, really! -- don't we in fact turn the Bible into a cipher for understanding Narnia? Sure, Lewis does some interesting stuff, and I've had some great discussion about his use of pagan imagery in concepts in Narnia and "Till We Have Faces," but Narnia isn't Scripture. If we want to use his books as a springboard to discussion of larger biblical issues -- Is Aslan's liberation of those enstatued in the White Witch's castle an accurate representation of what happened when Christ descended into hell? What are some ways we've been ensorceled by society like Prince Rilian was? -- I say, that's fine.
But especially when it comes to the allegorical elements of "Wardrobe," the eschatological matters of "The Last Battle," the depiction of Aslan and even the presence of Emeth in "The Last Battle," we need to remember that these are Lewis' understandings of what the Bible teaches, and he may in fact be wrong. Using his writings as the underpinnings for a Bible study means projecting his views, conceits, and doctrines back onto the biblical texts, and that's a risky proposition.
Just my 2 cents.