5 But after he had said, “in place of loving me, they detracted from me;” what does he add? “But I gave myself unto prayer.” He said not indeed what he prayed, but what can we better understand than for them themselves? For they were detracting greatly from Him whom they crucified, when they ridiculed Him as if He were a man, whom in their opinion they had conquered; from which Cross He said, “Father, forgive them, for they know not what they do;” so that while they in the depth of their malignity were rendering evil for good, He in the height of His goodness was rendering good for evil....The divine words then teach us by our Lord's example, that when we feel others ungrateful to us, not only in that they do not repay us with good, but even return evil for good, we should pray; He indeed for others who were raging against Him, or in sorrow, or endangered in faith; but we for ourselves in the first place, that we may by the mercy and aid of God conquer our own mind, by which we are borne on to the desire of revenge, when any detraction is made from us, either in our presence or our absence....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)