Jesus then goes on to discuss particulars, starting with the Sixth Commandment, "You shall not murder." When He says "You have heard that it was said of old . . ." (Matt. 5:21; NKJV), the reference is to an idea stated in a tractate in the Mishnah entitled "Aboth" ("Fathers"). Aboth describes a chain of tradition that allegedly extends from Moses through a long succession of rabbis down to a certain Judah the Patriarch, who was the apparent compiler of the Mishnah in the Second Century A.D. The Pharisees in particular relied on this oral tradition to supplement their understanding of the Torah.
What was said to "those of old" was "You shall not murder, and whoever murders will be in danger of the judgment." The first clause is, of course, the Sixth of the Ten Commandments, and is in the Bible. The second clause ("whoever murders will be in danger of the judgement") is a brief synopsis of the treatment of the subject in the Mishnah. The tractate Sanhedrin discusses a number of different scenarios and makes a pronouncement on each. "If a murderer had struck his fellow with a stone or with [an instrument of] iron, or if he had pressed him down into the water or into the fire and he could not arise out of it, and he died, he is culpable." But, "if he pushed him [and he fell] into the water or into the fire and he could arise out of it, and yet he died, he is not culpable" (Sanh. 9:1).
But according to Jesus this misses the whole point. While the Sanhedrin obviously had to make decisions about the individual cases that came before it, what was largely missing in the legal discussions was the intent of the Law. The underlying principle of the law concerning murder was stated in Lev. 19:17,18: "You shall not hate your brother in your heart. You shall surely rebuke your neighbor, and not bear sin because of him. You shall not take vengeance, nor bear any grudge against the children of your people, but you shall love your neighbor as yourself: I am the Lord." In other words, the intent of the precept is not simply that we should avoid certain circumstances that might lead to the death of the victim, but rather that we should have an active concern for his wellbeing. We are to love our neighbors as ourselves.
Jesus draws attention to the underlying motive of murder, which is anger. "But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment . . ." (v. 22). While man looks on the outward appearance, God looks on the heart; and from God's perspective, the difference between the heart of a murderer and the heart of a person with "anger management issues" is virtually indistinguishable. If the only reason we do not act on our impulses is because we fear civil punishment, that hardly makes us moral persons. An evil desire springs from an evil heart, and the heart lies fully exposed to God's view.
But it is not just a matter of escaping the censure of the civil authorities. It is ultimately God with Whom we have to do. Jesus reminds His listeners "Whoever says 'You fool!' shall be in danger of hell fire." "Gehenna" (from the Hebrew for "The Valley of Hinnom") was a valley just outside of Jerusalem where children were once sacrificed by fire to the pagan deity Moloch. It was a vivid symbol of eternal punishment. The implication here is that we are not just dealing with whatever punishment the civil authorities might mete out. Rather we face an offended God Who is able to punish us in hell.
Jesus then tells us what we must do. If we are making an offering at the altar at the temple, and we remember that we have offended someone, before we proceed with the offering, we should go and seek reconciliation with the offended brother, and then return to offer our gifts. In other words, the offering means nothing if our conduct is not right. Here Jesus is echoing the thought of Psalm 51:16,17). "For You do not desire sacrifice, or else I would give it; You do not delight in burnt offering. The sacrifices of God are a broken spirit, A broken and contrite heart – These, O God, You will not despise."
In the sight of God a shallow religious formalism will not do. What God wants to see is a religious profession backed up by a right attitude and right behavior. It is the way we live that counts, not what we say. The danger of our time is to keep up the pretense of religious profession, while accommodating our lives to the secular and materialistic spirit of the age. We are deceiving no one but ourselves.