Francis Schaeffer's classic - He Is There and He Is Not Silent.
This sentence was so simple, but so profound and practical for most Christians:
"You have to preach the simple gospel so that it is simple to the person to whom you are talking, or it is no longer simple."
That is brilliant. Whether you're talking to a middle schooler or a person who has never been to church or a true post modern... simple to them is WAY different than the way most people generally explain the gospel "simply".
"So why have we as Christians gone on saying the great truths in ways that nobody understands? Why do we keep talking to ourselves, if men are lost and we say we love them."
- Francis Schaeffer
Why do we keep talking to ourselves? Because it's just easier? Because we never really think about it?