11 And see how He proceeds little by little in His punishments, all but excusing Himself unto you, and signifying that His desire indeed is to threaten nothing of the kind, but that we drag Him on to such denunciations. For observe: “I bade you,” says He, “not be angry for nought, because you are in danger of the judgment. You have despised the former commandment: see what anger has produced; it has led you on straightway to insult, for you have called your brother 'Raca.' Again, I set another punishment, 'the council.' If you overlook even this, and proceed to that which is more grievous, I visit you no longer with these finite punishments, but with the undying penalty of hell, lest after this you should break forth even to murder.” For there is nothing, nothing in the world more intolerable than insolence; it is what has very great power to sting a man's soul. But when the word too which is spoken is in itself more wounding than the insolence, the blaze becomes twice as great. Think it not then a light thing to call another “fool.” For when of that which separates us from the brutes, and by which especially we are human beings, namely, the mind and the understanding—when of this you have robbed your brother, you have deprived him of all his nobleness.
Let us not then regard the words merely, but realizing the things themselves, and his feeling, let us consider how great a wound is made by this word, and unto how much evil it proceeds. For this cause Paul likewise cast out of the kingdom not only “the adulterous” and “the effeminate,” but “the revilers” also. And with great reason: for the insolent man mars all the beauty of charity, and casts upon his neighbor unnumbered ills, and works up lasting enmities, and tears asunder the members of Christ, and is daily driving away that peace which God so desires: giving much vantage ground unto the devil by his injurious ways, and making him the stronger. Therefore Christ Himself, cutting out the sinews of the devil's power, brought in this law.
For indeed He makes much account of love: this being above all things the mother of every good, and the badge of His disciples, and the bond which holds together our whole condition. With reason therefore does He remove with great earnestness the roots and the sources of that hatred which utterly spoils it.
Think not therefore that these sayings are in any wise hyperbolical, but consider the good done by them, and admire the mildness of these laws. For there is nothing for which God takes so much pains, as this; that we should be united and knit together one with another. Therefore both in His own person, and by His disciples, as well those in the Old, as in the New Testament, He makes so much account of this commandment; and is a severe avenger and punisher of those who despise the duty. For in truth nothing so effectually gives entrance and root to all wickedness, as the taking away of love. Wherefore He also said, “When iniquity abounds, the love of the many shall wax cold.” Thus Cain became his brother's murderer; thus Esau; thus Joseph's brethren; thus our unnumbered crimes have come revelling in, this bond being dissevered. You see why He Himself also roots out whatever things injure this, on every side, with great exactness.
Source: Homilies on the Gospel of St. Matthew (New Advent)