1 Thessalonians 5:15

15See that no one render evil for evil. As it is difficult to observe this precept, in consequence of the strong bent of our nature to revenge, he on this account bids us take care to be on our guard. For the word see denotes anxious care. Now, although he simply forbids us to strive with each other in the way of inflicting injuries, there can, nevertheless, be no doubt that he meant to condemn, at the same time, every disposition to do injury. For if it is unlawful to render evil for evil, every disposition to injure is culpable. This doctrine is peculiar to Christians — not to retaliate injuries, but to endure them patiently. And lest the Thessalonians should think that revenge was prohibited only towards their brethren, he expressly declares that they are to do evil to no one. For particular excuses are wont to be brought forward in some cases. “What! why should it be unlawful for me to avenge myself on one that is so worthless, so wicked, and so cruel?” But as vengeance is forbidden us in every case, without exception, however wicked the man that has injured us may be, we must refrain from inflicting injury.

But always follow benignity. By this last clause he teaches that we must not merely refrain from inflicting vengeance, when any one has injured us, but must cultivate beneficence towards all. For although he means that it should in the first instance be exercised among believers mutually, he afterwards extends it to all, however undeserving of it, that we may make it our aim to overcome evil with good, as he himself teaches elsewhere. (Romans 12:21) The first step, therefore, in the exercise of patience, is, not to revenge injuries; the second is, to bestow favors even upon enemies.