One of the things that surprised me when I first read the New Testament seriously was that it talked so much about a Dark Power in the universe—a mighty evil spirit who was held to be the Power behind death and disease, and sin. The difference is that Christianity thinks this Dark Power was created by God, and was good when he was created, and went wrong. Christianity agrees with Dualism that this universe is at war. But it does not think this is a war between independent powers. It thinks it is a civil war, a rebellion, and that we are living ma part of the universe occupied by the rebel.
Enemy-occupied territory—that is what this world is. Christianity is the story of how the rightful king has landed, you might say landed in disguise, and is calling us all to take part in a great campaign of sabotage. When you go to church you are really listening--in to the secret wireless from our friends: that is why the enemy is so anxious to prevent us from going. He does it by playing on our conceit and laziness and intellectual snobbery. I know someone will ask me, ‘Do you really mean, at this time of day, to re-introduce our old friend the devil-—hoofs and horns and all?’ Well, what the time of day has to do with it I do not know. And I am not particular about the hoofs and horns. But in other respects my answer is ‘Yes, I do. I do not claim to know anything about his personal appearance. If anybody really wants to know him better I would say to that person. ‘Don’t worry. If you really want to, you will. Whether you’ll like it when you do is another question.’
Quotes from Mere Christianity, Part 16
C.S. Lewis, Mere Christianity (1952; Harper Collins: 2001) 45-46.