14 And this indeed, as we have said, is a prophecy, not a wish....And the Lord in the Gospel has set before us the widow for an example, who longing to be avenged, did intercede with the unjust judge, who at length heard her, not as being guided by justice, but overcome with weariness: but this the Lord has set before us, to show that much more the just God will speedily make the judgment of His elect, who cry unto Him day and night. Thence is also that cry of the Martyrs under the altar of God, that they may be avenged in the judgment of God.
Where then is the, “Love your enemies, do good unto them that hate you, and pray for them that persecute you”? Where is also the, “Not rendering evil for evil, nor cursing for cursing:” and, “unto no man rendering evil for evil”?...For when the Lord was exhorting us to love enemies, He set before us the example of our Father, who is in Heaven, “who makes His sun to rise upon good men and evil men, and rains upon just men and unjust men:” does He yet therefore not chasten even by temporal correction, or not condemn at the last the obstinately hardened?
Let therefore an enemy be so loved as that the Lord's justice whereby he is punished displease us not, and let the justice whereby he is punished so please us, as that the joy is not at his evil but at the good Judge. But a malevolent soul is sorrowful, if his enemy by being corrected shall have escaped punishment: and when he sees him punished, he is so glad that he is avenged, that he is not delighted with the justice of God, whom he loves not, but with the misery of that man whom he hates: and when he leaves judgment to God, he hopes that God will hurt more than he could hurt: and when he gives food to his hungering enemy, and drink to him thirsty, he has an evil-minded sense of that which is written, “For thus doing you shall heap coals of fire upon his head.”...In such sort then under the appearance of one asking in this Psalm, future vengeance on the ungodly is prophesied of, as that we are to understand that holy men of God have loved their enemies, and have wished no one anything but good, which is godliness in this world, everlasting life in that to come; but in the punishments of evil men, they have taken pleasure not in the ills of them, but in God's good judgments; and wheresoever in the holy Scriptures we read of their hatreds against men, they were the hatreds of vices, which every man must needs hate in himself, if he loves himself.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)