Why do we lie, or fail to love, or break our promises, or live selfishly? Of course, the general answer is “Because we are weak and sinful,” but the specific answer is that there is something besides Jesus Christ that we feel we must have to be happy, something that is more important to our heart than God, something that is enslaving our heart through inordinate desires. The key to change (and even to self-understanding) is therefore to identify the idols of the heart. Tim Keller, The Gospel in Life: Grace Changes Everything