The Fifth Commandment

Matthew 5:21-22
21 “You have heard that it was said to those of old, ‘You shall not murder; and whoever murders will be liable to judgment.’ 22 But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, ‘You fool!’ will be liable to the hell of fire.

Large Catechism
[186] The meaning of this commandment, then, is that no one should harm another person for any evil deed, no matter how much that person deserves it.

Large Catechism
[183] But the occasion and need for this commandment is that, as God well knows, the world is evil and this life is full of misery. Therefore he has erected this and the other commandments to separate good and evil.