The series is openly a metaphore for Christianity. As I understand it, C.S. Lewis wrote the novels as a way to teach children the Gospel through story. I have been so impresed by C.S. Lewis' gospel insight, and remarkable writing, that from time-to-time after reading to Grace I've re-read passages to Erin. For instance, here are the last few paragraphs from the final chapter of The Voyage of the Dawn Treader:
"Oh, Aslan," said Lucy. "Will you tell us how to get into your country from our world?"
"I shall be telling you all the time," said Aslan. "But I will not tell you how long or short the way will be; only that it lies across a great river. But do not fear that, for I am the great Bridge Builder."
When Lucy asks if Aslan is in her world (England), Aslan states that he is,
"But there I have another name, You must learn to know me by that name. This was the very reason why you were brought to Narnia, that by know me here for a little, you may know me better there."There are dozens of deep gospel metaphores, most deeper than what I've quoted above (I only quote this one because we read it just the other night). I've become a great admirer of C.S. Lewis. His writting is excellent, and his treatment of Christianity is some of the best non-scripture teaching I've ever read.