Although Lewis wrote the Chronicles of Narnia with children in mind, he also wanted the stories to appeal to adults and to convey a larger message. Thus the story of Narnia can be read and enjoyed on another level, as the story of Christianity as it is told in the Bible. Aslan the lion represents Jesus Christ, who died as a sacrifice to God for the sins of all people and then came back to life before ascending into heaven.
In 1954 Lewis explained it this way in a letter to some Maryland 5th graders: "I said, 'Let us suppose that there were a land like Narnia and that [Jesus], as he became a Man in our world, became a Lion there, and then imagine what would happen.'"