Raised in a church-going family in the Church of Ireland, Lewis claimed he became an atheist at the age of 15, though in contradiction he later described his young self as being "very angry with God for not existing". He returned to his Christian beliefs at age 33.
His separation from Christianity began when he started to view his religion as a chore and as a duty; Lewis's interest in fantasy and mythology, especially in relation to the works of George MacDonald, was part of what turned him from atheism. In fact, MacDonald's position as a Christian fantasy writer was very influential on Lewis.
Influenced by arguments with his Oxford colleague and friend J. R. R. Tolkien, and by the book The Everlasting Man by Roman Catholic convert G. K. Chesterton, he slowly rediscovered Christianity. He fought greatly up to the moment of his conversion noting, "I came into Christianity kicking and screaming."
After his conversion to theism in 1929, Lewis converted to Christianity in 1931. Following a long discussion and late-night walk with his close friends Tolkien and Hugo Dyson, he records making a specific commitment to Christian belief while on his way to the zoo with his brother. He became a member of the Church of England — somewhat to the disappointment of Tolkien, who had hoped he would convert to Roman Catholicism (Carpenter 2006).[2]
His most famous works, the Chronicles of Narnia, contain many strong Christian messages and are often considered allegory. Lewis, an expert on the subject of allegory, maintained that the books were not allegory, and preferred to call the Christian aspects of them "suppositional". As Lewis wrote in a letter to a Mrs. Hook in December 1958:
If Aslan represented the immaterial Deity in the same way in which Giant Despair [a character in The Pilgrim's Progress] represents despair, he would be an allegorical figure. In reality however he is an invention giving an imaginary answer to the question, 'What might Christ become like, if there really were a world like Narnia and He chose to be incarnate and die and rise again in that world as He actually has done in ours?' This is not allegory at all. (Martindale & Root 1990)
The books (on Narnia) contain many allusions to Christian ideas which are easily accessible to younger readers; however, the books are not weighty, and can be read for their adventure, colour, and richness of ideas alone.