“The Bible says, “Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image” (Genesis 9:6). Is God saying that it’s right to kill murderers?”
This verse shows how much God hates murder. The Bible is consistent. When one of his disciples tried to defend him with violence, Jesus said ‘Put your sword back into its place. For all who take the sword will perish by the sword’ (Matthew 26:52).
So should murderers be put to death?
The Law of Moses was the civil and religious law which God gave to His people Israel, to govern their life as His nation in the time of the Bible’s Old Testament. It’s recorded in the books of Exodus through to Deuteronomy. Under the Law, the penalty for murder was execution (Exodus 21:12).
We are no longer living under the Law of Moses. Christians live under the law of Christ. Christ told us to live peacefully and not to avenge ourselves. For example, ‘Do not resist the one who is evil. But if anyone slaps you on the right cheek, turn to him the other also’ (Matthew 5:39). As the Apostle Paul explains: ‘Repay no one evil for evil, but give thought to do what is honourable in the sight of all. If possible, so far as it depends on you, live peaceably with all. Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, “Vengeance is mine, I will repay, says the Lord.” To the contrary, “if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by so doing you will heap burning coals on his head.” Do not be overcome by evil, but overcome evil with good‘ (Romans 12:17–21).
When God told the magistrates in Israel to operate the death penalty for murder, that was what they needed to do. When He tells us not to avenge ourselves, that is what we must do.
Even in Old Testament times, God showed that He is a God of mercy. For example Cain in Genesis 4 and David in 2 Samuel 11 both committed murder. God could have imposed the death sentence, but He did not. This is a precedent we are to follow, in big matters and also in small matters: ‘For judgement is without mercy to one who has shown no mercy. Mercy triumphs over judgement’ (James 2:13).
Some countries operate the death penalty, and some countries don’t. That is their prerogative, it’s not the Christian’s business.