This command might be, for most people, both the easiest and hardest to obey. The vast majority of us have never physically committed murder, so we might be tempted to move on to the next one. Of course, if we’re familiar with Jesus’ Sermon on the Mount, then we see that we aren’t off the hook just because we've never pulled a trigger on someone. First we’ll deal with some modern misinterpretations, and then we’ll examine how the Lord Jesus understood it.
The first question a modern person might ask is “Does this outlaw capital punishment by the state?” The short answer is no. Anyone who has claimed that it does probably has never read the rest of the Torah. In fact, the very next chapter in Exodus explicitly orders capital punishment for at least four crimes, and you can make the argument for two others (killing a slave and causing a miscarriage). There are some biblical passages which one can use to argue against the death penalty, but this isn’t one of them.
How the Jews interpreted this verse is a classic study in legalism. The way that they interpreted this command (and which Jesus seeks to correct) was that as long as you didn’t physically kill someone, you weren’t guilty of breaking it. Then along came our Savior to rectify this misunderstanding: Every physical murder started with a thought. God is not just concerned with our actions but with the thoughts and attitudes which lead to those actions. The attitudes that he condemned were both unjustified anger and the degrading of another person’s dignity as created in God’s image. The word Raca was an Aramaic term of contempt, literally “empty head,” or roughly equivalent to “stupid idiot.” This passage probably doesn’t say that calling someone foolish is necessarily a bad thing (Paul did it in Galatians), but what Jesus seemed to be warning against is a mind-set of disregarding the infinite value of an image-bearer. This is why the Lord's commands to Noah post-flood include capital punishment for murder: Because we are made in God's image, the ultimate crime of taking a life requires (at least in some circumstances) the ultimate punishment.
Based on the context in Jesus' sermon, the anger which we need to avoid is settled anger or bitter resentment, not simply being angry at someone. To summarize, in order to follow his instruction, we need not only to avoid physical murder, but value the image of God placed on every person we meet.
Lord Jesus, your word is pretty disturbing at times. Change me, please.