“You have heard that it was said to those of old, ‘You shall not murder; and whoever murders will be liable to judgment.’ 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. (Matthew 5:21-22)
Here we observe first, that Christ attacks a sin called anger, which is very common and powerfully rules the world. And it is not one of the gross, public vices punished also by the world, but one of those fine sins of the devil that do not want to pass for sin. For they sail under false colors, so that no one can rebuke and punish them. For instance, pride will not be called pride, but truth and justice; envy and hatred do not want to be reprimanded, but rather extolled as being true earnestness and godly zeal against wickedness. These are really the two colors the devil carries in his realm, namely, lying and murder, which in the eyes of the world claim the honor and praise of being holiness and righteousness in the highest degree.
For this reason, our Lord and Savior singles out the Pharisees, who fain would be the holiest and most pious, and be so considered by everybody; he even calls their doings by the beautiful name of righteousness, but he pictures and judges it as one not leading to heaven but into the abyss of perdition, a veritable fruit of Satan. And this he does for the reason that they wanted to be called righteous and pious, defying the whole world to prove the contrary, and at the same time were filled with venomous wrath, envy and hate. The world cannot see nor judge in such matters, therefore Christ alone is the judge here who dare and can pass such a sentence of judgment. Even if this righteousness of the Pharisees be ever so beautiful and holy, yet, they shall not enter into the kingdom of heaven; for I do not desire nor will have a righteousness that stamps itself as such, and will not be called sin, but struts about in the fine coat of divine righteousness, so that we must call them Christian, pious people, holy spiritual fathers, etc.
Now, on what is this righteousness of the Pharisees based and where does it derive its name? On the fact that God said, "Thou shalt not kill," etc. On these words they planted themselves and stood. The text says nothing more than "Thou shalt not kill;" hence it follows that whoever does not kill, is righteous. But when my feelings are hurt and I am wronged, I have good grounds and reasons for being wrought up and for resenting the injustice; at the same time my wrath appears doubly justified because it suffers violence and injustice without actually killing. This wrath of mine advances a step by embellishing its cause in proclaiming its innocence and parading its piety before God and the world thus: Have I not good reasons for being angry? This and that my neighbor has done to me in return for my many favors, and I would have gladly given him my life's blood; this is the thanks, the returns, with which lie pays me. Am I to suffer all this and pass such malice by? And at this point a Pharisee boldly proceeds to malign and persecute his neighbor in the highest degree, wherever he can, inflicting harm and injury; and all this is claimed to be done justly, he himself being pious and holy, yea, extolled as a martyr in the sight of God and men.
Christ here takes energetic action, and abolishes anger wholly and completely in the entire world, draws it to himself and says: I do not merely say, You shall not kill, but you shall in no case be angry; the one is as solemnly and earnestly prohibited as the other. For you are not told to judge or avenge yourself, and even though you are right and have a just cause, still your wrath is of the devil; as St. James in his Epistle, 1:20, says: “The wrath of man worketh not the righteousness of God.” Hence all anger is to be abolished entirely from us and the wrath of God alone is to work; otherwise it will turn out to be the devil's wrath and it certainly does not cool down without sin. Just as also these three: to judge, to avenge and to glory, have been taken from us, and no person should share in them, though they have ever so good a cause and ever so great holiness. But to God alone belong honor, judgment and vengeance, hence also wrath.