The Sermon on the Mount is a revolution in holiness. Jesus takes all the external issues and makes them first and foremost internal. He begins with a few examples of the most egregious sins: murder and adultery. This is a crowd that congratulates itself on staying far from such obvious crimes. But then Jesus says, “Oh—don’t think you’ve kept the command simply because you haven’t pulled the trigger. If you hate someone, you’ve murdered them in your heart. And as for sexual integrity—just because you haven’t actually ‘done it’ doesn’t mean you’re clean—have you wanted to, in your heart? Have you desired someone who wasn’t your spouse?”
This way of looking at goodness is mighty exposing. As it should be. Holiness, he is driving at, is a matter of the heart.