Our Gospel opens with Jesus telling us our righteousness must exceed that of the Scribes and Pharisees. It goes on then with Jesus telling us one way in which we must be more morally upright. Going beyond avoiding murdering anyone, he says that as Christians we cannot even be angry with people.
That advise about controlling anger is just one item in the carefully constructed Sermon on the Mount, a document we should consider in its entirety.
The Sermon on the Mount begins with Jesus going up on a mountain the way Moses went up on Mount Sinai. Next, it has Jesus giving us his Beatitudes just as Moses gave us the Ten Commandments. Then, Jesus tells us he had not come to abolish the old law. Rather, he came to complete its moral lessons.
Following on making that announcement, Jesus went on to describe six ways in which his new law goes beyond the old law. We have the first of them here. The old law forbade murder, the new law of Jesus forbids even being angry with our neighbor.
The next way that Jesus will tell us we must go beyond the old law is in the matter of sexual morality. The old law forbade adultery. Our Lord’s new law forbids lusting.
These contrasts between what is forbidden by the old and new law are referred to as the six “antitheses.” The other four have to do with divorce, oaths, vengeance and love of neighbor.