Why did Jesus say again and again in the Sermon on the Mount, “You have heard that it was said to those of old . . . But I say to you . . .” (Matthew 5:21–22)?

The Sermon on the Mount must be understood as Jesus’ exposition of Old Testament law, not a different moral standard altogether. He was simply refuting the Pharisees’ misconstrued teaching about the law’s moral precepts. Jesus was unpacking the true and full meaning of the law as it was originally intended—especially in contrast to the limited, narrow, and woodenly literal approach of the Pharisees. Their hermeneutic (the method by which they interpreted Scripture) led them to expound for hours on the law’s invisible fine points while inventing technical twists and turns to make exceptions to some of the law’s most important moral precepts.