We must guard also against a visible enemy when he incites us by silence; by the help of which alone we can escape from those greater than ourselves, and maintain that humility which we must display towards all.
17. But we must also guard against him who can be seen, and who provokes us, and spurs us on, and exasperates us, and supplies what will excite us to licentiousness or lust. If, then, any one reviles us, irritates, stirs us up to violence, tries to make us quarrel; let us keep silence, let us not be ashamed to become dumb. For he who irritates us and does us an injury is committing sin, and wishes us to become like himself.
18. Certainly if you are silent, and hidest your feelings, he is wont to say: “Why are you silent? Speak if you dare; but you dare not, you are dumb, I have made you speechless.” If you are silent, he is the more excited. He thinks himself beaten, laughed at, little thought of, and ridiculed. If you answer, he thinks he has become the victor, because he has found one like himself. For if you are silent, men will say: “That man has been abusive, but this one held him in contempt.” If you return the abuse, they will say: “Both have been abusive.” Both will be condemned, neither will be acquitted. Therefore it is his object to irritate, so that I may speak and act as he does. But it is the duty of a just man to hide his feelings and say nothing, to preserve the fruit of a good conscience, to trust himself rather to the judgment of good men than to the insolence of a calumniator, and to be satisfied with the stability of his own character. For that is: “To keep silence even from good words;” since one who has a good conscience ought not to be troubled by false words, nor ought he to make more of another's abuse than of the witness of his own heart.
19. So, then, let a man guard also his humility. If, however, he is unwilling to appear too humble, he thinks as follows, and says within himself: “Am I to allow this man to despise me, and say such things to my face against me, as though I could not open my mouth before him? Why should I not also say something whereby I can grieve him? Am I to let him do me wrong, as though I were not a man, and as though I could not avenge myself? Is he to bring charges against me as though I could not bring together worse ones against him?”
20. Whoever speaks like this is not gentle and humble, nor is he without temptation. The tempter stirs him up, and himself puts such thoughts in his heart. Often and often, too, the evil spirit employs another person, and gets him to say such things to him; but do thou set your foot firm on the rock. Although a slave should abuse, let the just man be silent, and if a weak man utter insults, let him be silent, and if a poor man should make accusations, let him not answer. These are the weapons of the just man, so that he may conquer by giving way, as those skilled in throwing the javelin are wont to conquer by giving way, and in flight to wound their pursuers with severer blows.
Source: On the Duties of the Clergy (New Advent)