You have to show people that it takes faith to doubt Christianity. C. S. Lewis argued with God before his conversion that the universe seems so cruel and unjust. But then he asked himself, "But how had I got this idea of just and unjust? What was I comparing this universe with when I called it unjust? . . . Atheism turns out to be too simple" (Mere Christianity, Book 2, Part 1). In the natural world the strong eat the weak, and there's nothing wrong with violence. Where do you get the standard that says the human world shouldn't work that way, that says the natural world is wrong? You can only judge suffering as wrong if you're using a standard higher than this world, a supernatural standard. If there's no God, you have no reason to be upset at the suffering in this world. It takes faith to get mad at this world.Read the rest.
Books by Tim Keller:
The Prodigal God
Gospel in Life: Grace Changes Everything
The Reason for God