Murder: The Sixth Commandment
The way Jesus handles this material is by contrasts (“You have heard that it was said … but I tell you …”), and the point at which these contrasts begin is the sixth commandment. Ever since Sinai, the Jews had known “you shall not murder”; it was part of God’s law. But the leaders of the people had joined that commandment (found in Exod. 20:13) to Numbers 35:30, which demanded death for murderers, implying that the sixth commandment referred only to the specific act of killing.
Is that all murder is? asked Jesus. Is it nothing but killing? Suppose a man wants to kill his enemy but is stopped by some unexpected circumstance. Is he innocent just because he didn’t get a chance to follow through on his desire? Suppose he is too cowardly to kill but would like to do it. Or suppose he is just afraid of getting caught. What if he only hates his enemy? Or insults him? Is he still innocent of breaking this commandment?
No, says Jesus. In a human court the only acts that can be judged and punished are external acts, because human beings can look only on outward things. They cannot see the heart. But in God’s court “anyone who is angry with his brother will be subject to judgment,” and anyone who merely says, “ ‘You fool!’ will be in danger of the fire of hell” (v. 22).
This is not earth-shatteringly new, of course. The Pharisees and other teachers of the law should have discovered this deeper meaning of the sixth commandment by themselves. William Hendriksen observed rightly,
There was no excuse for the fact that in their interpretation of the sixth commandment the scribes and Pharisees of Jesus’ day, in agreement with the men of long ago, were omitting the main lesson. Moses had emphasized love for God (Deut. 6:5) and for man (Lev. 19:18). Not only that but the very first domestic quarrel narrative, the story of Cain and Abel, had in a very impressive manner pointed up the evil of jealous anger, as being the root of murder (Gen. 4:1–16). … Accordingly Jesus, in interpreting the sixth commandment as he does, far from annulling it, is showing what it had meant from the very beginning.
There is something else in these verses. It is true that they interpret the sixth commandment definitively. We now know exactly what the words “you shall not murder” mean. But in addition to that, Jesus also tells us what to do when we do become angry or when we know we have done something wrong to someone else. (1) We must make the wrong right, being reconciled to our brother (vv. 24–25); and (2) we must make things right immediately, even before we worship God (vv. 23–24).
The reason God comes into the picture is because the sin of anger, like all sins, is ultimately against God and must be made right before him. This is why Jesus talks about being “thrown into prison” until “you have paid the last penny” (vv. 25–26). It is not just a human prison he is thinking of. It is hell, which brings the end of the section (v. 26) back to what Jesus warned his hearers of at the beginning (v. 22).
James Montgomery Boice, The Gospel of Matthew (Grand Rapids, MI: Baker Books, 2001), 88–89.