Clive Staples Lewis was and remains a fascinating and inspirational intellectual, author and veteran of the First Great War.
The Chronicles of Narnia are first and foremost, literature for children. The premise of Narnia was based on C.S. Lewis' childhood fantasies and amateur writings, and the younger the audience member the stronger the connection to the young characters, their real-world plights and their fantastic escape to Narnia. He wrote himself in as a character (Diggory Kirk, I believe).
Lewis claimed to be the most reluctant convert of them all, but largely thanks to J.R.R. Tolkien Christian bookstores are still selling Lewis' reflections on life, conscience and faith.
He also wrote a sci-fi trilogy for more mature readers, if you've started to outgrow Narnia.