Western culture no longer takes seriously many of the Ten Commandments. The third and fourth commandments are certainly neglected. There is also a good argument that our society does not care much about the prohibitions against adultery (seventh commandment), theft (eighth commandment), slander (ninth commandment), or covetousness (tenth commandment) either. However, apart from abortion and euthanasia, there is no movement to legalize murder. In the modern West, people still want to hold that killing an innocent human being is wrong.
As we look at the sixth commandment, notice first that the ESV uses the word “murder,” not “kill.” That is because the Hebrew language has several words that mean “kill,” and the one that appears in the Hebrew text of today’s passage appears most often in the context of the deliberate taking of innocent life. Not every kind of killing is murder, which means that not all acts of killing are against God’s law. Exodus 22:2–3, for example, does not prescribe the death penalty if a person kills someone in self-defense when the person has no other recourse to protect his life and property. This indicates that killing in a legitimate act of self-defense is not murder and not forbidden by the sixth commandment. The concern in the commandment against murder is to protect innocent life, and in the case of self-defense, the innocent party is the one who must defend himself.
Over the centuries, Christians thinkers have seen a broader application of passages such as Exodus 22:2–3 to warfare, teaching that there are just wars in which Christians may participate and that states may wage war without violating the sixth commandment. Generally speaking, just war theory says that states may defend themselves against unlawful aggression in order to protect their people and territories. Sadly, nations do not always follow these guidelines, and tragically, the scourge of abortion on demand means that many countries do not take seriously the command not to allow the killing of innocent human beings. Christians are obliged, insofar as they are able, to hold the state to account for not fulfilling its responsibility to protect life (Rom. 13:1–7).
Finally, Jesus explains that the sixth commandment prohibits also those attitudes of the heart that lead to murder. Ungodly anger breaks the sixth commandment (Matt. 5:21–26).