At the very end of the Sermon on the Mount we read that the people who heard Jesus “were astonished at his doctrine; for he taught them as one having authority, and not as the scribes” (Matt. 7:28-29). The statement indicates that the unprecedented authority of the Lord Jesus Christ was startling to his contemporaries. But surprising as this note of authority was, the standard that Jesus set before men was more startling still. The men of Christ’s day, like those of our time, were for the most part content with an external righteousness or goodness. By contrast, Jesus taught that the only righteousness acceptable to God is a divine righteousness that in time brings about a full transformation of the personality.
Up to the twentieth verse of Matthew 5, the demand for an internal righteousness has been presented positively. For Christ had spoken of the character of the Christian man. He is poor in spirit, sorrowful for sin, meek, hungry and thirsty for righteousness, merciful, pure in heart, a peacemaker, persecuted. And because of this he is to be the salt of the world and its light. Now, with verse 21 this changes; the positive side is dropped, and Jesus begins to state the same thing negatively.
For centuries, the scribes and Pharisees had been teaching that to avoid murder was to keep the sixth commandment. Jesus taught that men have broken the commandment even if they have only been angry with one another or called one another a fool. The scribes had taught that the seventh commandment was kept if a person avoided sleeping with another man’s wife or another woman’s husband. Jesus taught that the commandment was broken even if adultery existed only as a thought in the heart. A man’s word must be kept in spirit as well as in letter, according to Jesus. Charity must go beyond the call of mere duty. A man’s enemies must be loved by him as well as his neighbors and friends.
In the remainder of chapter 5, six of these themes are introduced, in each case by the formula, “Ye have heard that it was said by them of old time” or “ye have heard that it hath been said.” In each case the points are similar: True Christian morality must arise from the heart, and, as a result of this, no one but God (who controls the heart) can provide it.