4 “Hear Thou, O God, my entreaty, and despise not my prayer: give heed unto me, and hearken unto me”. Of one earnest, anxious, of one set in tribulation, are these words. He is praying, suffering many things, from evil yearning to be delivered: it remains that we hear in what evil he is, and when he begins to speak, let us acknowledge there ourselves to be; in order that the tribulation being shared, we may conjoin prayer. “I have been made sad in my exercise, and have been troubled”.
Where made sad, where troubled? “In my exercise,” he says. Of evil men, whom he suffers, he has made mention, and the same suffering of evil men he has called his “exercise.” Think ye not that without profit there are evil men in this world, and that no good God makes of them. Every evil man either on this account lives that he may be corrected, or on this account lives that through him a good man may be exercised. O that therefore they that do now exercise us would be converted, and together with us be exercised!
Nevertheless, so long as they are such as to exercise, let us not hate them: because in that wherein any one of them is evil, whether unto the end he is to persevere, we know not; and ofttimes when to yourself you seem to have been hating an enemy, you have been hating a brother, and know not. The devil and his angels in the holy Scriptures have been manifested to us, that for fire everlasting they have been destined. Of them only must amendment be despaired of....Therefore since this rule of Love for you is fixed, that imitating the Father you should love an enemy: for, He says, “love your enemies:” in this precept how would you be exercised, if you had no enemy to suffer?
You see then that he profits you somewhat: and let God sparing evil men profit you, so that thou show mercy: because perchance thou too, if you are a good man, out of an evil man hast been made a good man: and if God spared not evil men, not even you would be found to return thanks. May He therefore spare others, that has spared you also. For it were not right, when you had passed through, to close up the way of godliness.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)