Analogy

(From livingwaters, though I’ve heard it elsewhere):

Imagine you are standing in front of a judge, guilty of multiple serious crimes.  All the evidence has been presented and there is no doubt about your guilt.  Your apologies and good works cannot erase your crimes; therefore you must be punished.  The fine for your crime is $250,000 or imprisonment, but you don’t have two pennies to rub together. The judge is about to pass sentence (he can’t just let you off, even if you’re sorry, or he’d be a corrupt judge) someone you don't even know steps in and pays your fine for you! The court accepts the money and declares that you are free to go. The law has been satisfied, your debt has been paid in full, and the stranger’s sacrifice was a demonstration of his love.  That’s what God did for you 2000 years ago.  Jesus Christ paid your debt, out of love for you.

Take that analogy one step further: It wasn’t just a fine that was paid.  The penalty was death, not money, and still Jesus took your place.