After giving the wronged person the good advice, Saint Paul goes on to give him advice of a higher tone, telling him not to be overcome with evil but overcome evil with good. For he knew that even if the enemy was a brute he would not go on being an enemy once he was fed.
To overcome evil with good is true victory because the evil man who is overcome by good is set free, not from an exterior, foreign evil but from an interior, personal one, by which he is more grievously and ruinously laid waste than he would be by the inhumanity of any enemy from without.
So, it will do us much good if we refrain from evil. The person who appears to be overcome by evil for a time in fact may be overcoming evil, just as the Savior overcame evil by not resisting it. Evil, because is a distortion, works against itself, and when it is overcome it thinks that it has won! That’s why our enemy acts in such a way as to divert us from our purpose, looking for an opportunity to make us sin to fall in distortion. Therefore if we are provoked by him and do not reply in kind, we overcome him with good.
Based on Saint John Chrysostom, Augustine, Romans 12:21