If we want to kill sin, we must aim at the right target. That target is not merely bad behavior but the sinful desires of the heart that produce the behavior. Mortifying sin will certainly bring about changes in what we say and do, but we need more than external reformation. Many people change their behavior without changing their heart to any significant degree. But Jesus is concerned about the root and motivation of sinful behavior—our drives and desires—not simply the behavior itself. For example,