The King's Campaign of Sabotage

C.S. Lewis on the church in enemy territory:

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 to the secret wireless from our friends; that is why the enemy is so anxious to prevent us from going.

When a young man who has been going to church in a routine way honestly realizes that he does not believe in Christianity and stops going - provided he does it for honesty's sake and not just to annoy his parents - the spirit of Christ is probably nearer to him then than it ever was before. (Mere Christianity)