I wonder if you noticed the dedication at the beginning of The Lion, the Witch and the Wardrobe? C S Lewis wrote the story for his Goddaughter, Lucy Barfield. He was a committed Christian, and his lovely Chronicles of Narnia may have been his way of fulfilling his promise, as Lucy's Godfather, to help ensure that she received a Christian upbringing.
So how does Christianity fit into Narnia?
You don't have to be too familiar with the main Bible stories to recognise some of the key characters and themes. Without doubt, Aslan represents Jesus Christ, and also God Himself, and perhaps the White Witch represents Satan. Narnia, then, where the adventure happens, might also represent the Kingdom of God, as well as the Kingdom of Aslan.
Clearly, there is no direct retelling of any of the Bible stories, but if you look, you will find elements taken and retold for younger readers, in that special C S Lewis way. Do you remember how Edmund arrives in Narnia alone, disgruntled with his brother and sisters, and immediately meets with the White Witch in the forest? He is tempted with the enchanted Turkish Delight, and the promise of becoming a prince of Narnia:
'I think I would like to make you the Prince - some day, when you bring the others to visit me.'
Succumbing to temptation is a very powerful theme in the Bible. Jesus is tempted by Satan in the wilderness with promises of great power. Also Judas betrays Jesus, much as Edmund betrays his brother and sisters later in the story.
Of course, Edmund is rescued from the White Witch by Aslan, and although she later claims the life of Edmund as rightfully belonging to her, Aslan offers his own life in exchange for Edmund's. This action exactly follows that of Jesus Christ who died on the cross to save mankind.
You will also recognise the resurrection of Jesus Christ in the resurrection of Aslan, after his humiliation and execution by the Witch and her rabble of followers.
The Chronicles of Narnia will always be, first and foremost, a wonderful fantasy series for children. Even without reference to any of the religious symbolism, the characters set high standards of personal behaviour:
Edmund shook hands with each of the others and said to each of them in turn, "I'm sorry," and everyone said, "That's all right." And then everyone wanted very hard to say something which would make it quite clear that they were all friends with him again - something ordinary and natural - and of course no one could think of anything in the world to say.
But perhaps the key to the lasting success of the Chronicles of Narnia is the fact that they can be read and re-read on many levels and by readers of all ages.
CS Lewis did not write the Chronicles in chronological order. The Lion, the Witch and the Wardrobe was the first title that he wrote, and perhaps the most successful, but I list them here in the recommended order of reading: