But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath upon the one who practices evil. (13:4b)
In order to promote and protect the good in society, human government must punish the evil. Consequently, those who do what is evil have reason to be afraid.
Because the sword is an instrument of death, the weapon here symbolizes the right of civil government to inflict punishment, including the ultimate penalty of death for crimes that deserve it. In the earliest period of human existence, the Lord instituted capital punishment. “Whoever sheds man’s blood, by man his blood shall be shed, for in the image of God He made man” (Gen. 9:6). When Jesus told Peter, “Put your sword back into its place; for all those who take up the sword shall perish by the sword” (Matt. 26:52), he was reminding His disciple that the penalty for his killing one of Jesus’ enemies would be to perish himself through execution, which the Lord here acknowledges would be justified.
When Paul stood before the Roman governor Festus and made his appeal to Caesar, he said, “If then I am a wrongdoer, and have committed anything worthy of death, I do not refuse to die” (Acts 25:11). In saying that, he acknowledged that capital punishment was sometimes justified and that he would willingly accept it if he were to be found guilty of a capital crime.
When a society rejects capital punishment for even the most serious crimes, including murder, it comes under blood guiltiness from God. After Cain killed Abel, “The Lord said to Cain, ‘Where is Abel your brother?’ And he said, ‘I do not know. Am I my brother’s keeper?’ And He said, ‘What have you done? The voice of your brother’s blood is crying to Me from the ground’ ” (Gen. 4:10). Like Satan, whom he unknowingly had come to serve, Cain was both a murderer and a liar (see John 8:44). Immediately after the Flood, God established the divine law of capital punishment for murder (Gen. 9:6). As part of the Mosaic law, God declared, “You shall not pollute the land in which you are; for blood pollutes the land and no expiation can be made for the land for the blood that is shed on it, except by the blood of him who shed it” (Num. 35:33).
Among other things, Israel was sent into Babylonian captivity because of the many bloody crimes in the nation that went unpunished. “Make the chain,” God said, “for the land is full of bloody crimes, and the city is full of violence. Therefore, I shall bring the worst of the nations, and they will possess their houses. I shall also make the pride of the strong ones cease, and their holy places will be profaned” (Ezek. 7:23–24). When a nation does not administer justice, it eventually falls under God’s justice.