Think of Christ's resurrection as a store receipt. If you're in a department store and you buy some clothes, you should always ask for the receipt. Why? Because if you're still walking around the store a plainclothes security person could stop you and ask, "Excuse me, can I look in your bag?" And if you don't have a receipt you could get in trouble. So you if somebody stops you, you want to be able to hold up your receipt and say, "Oh, plainclothes security person, trouble me not because this proves that this has been paid for and I do not have to pay it again." The resurrection is a giant receipt stamped across history for all people to see, a receipt that allows you to know that your future is certain if you believe in Jesus Christ.
Editor's Note: In the same sermon, Tim Keller said, "If someone goes into jail because the law says that ten years in jail is the punishment for the crime, the day that man comes out of jail he has paid for the crime. That law doesn't have a claim on him anymore. He's free man. The wages of sin is death, and when Christ went down into death, he paid for our debt. When he came up out of the grave that meant it was paid. Christ's resurrection proves that it was fully paid."
