3 If you are angry against your neighbour, you are angry against God; and if you bear anger in your heart, against your Lord is your boldness uplifted. If in envy you rebuke, wicked is all your reproof. But if charity dwell in you, you have on earth no enemy. And if you are a true son of peace, you will stir up wrath in no man. If you are just and upright, you will not do wrong to your fellow. And if you love to be angry, be angry with the wicked and it will become you; if to wage war you seek, lo! Satan is your adversary; if you desire to revile, against the demons display your curses. If you should insult the King's image, you shall pay the penalty of murder; and if you revile a man, you revile the image of God. Do honour to your neighbour, and lo! You have honoured God. But if you would dishonour Him, in wrath assail your neighbour!
Source: On Admonition and Repentance (New Advent)