11 “For nothing You shall save them”. He has taught us even for these very men to pray. However “they shall sojourn and hide,” however deceitful they be, however dissemblers and liers in wait they be; do thou pray for them, and do not say, Shall God amend even such a man, so evil, so perverse? Do not despair: give heed to Him whom you ask, not him for whom you ask. The greatness of the disease do you see, the might of the Physician do you not see? “They shall sojourn and hide: as my soul has undergone.” Undergo, pray: and there is done what? “For nothing You shall save them.” You shall make them safe so as that nothing to You it may be, that is, so that no labour to You it may be. With men they are despaired of, but Thou with a word dost heal; You will not toil in healing, though we are astounded in looking on. There is another sense in this verse, “For nothing You shall save them:” with not any merits of their going before You shall save them....They shall not bring to You he-goats, rams, bulls, not gifts and spices shall they bring You in Your temple, not anything of the drink-offering of a good conscience do they pour thereon; all in them is rough, all foul, all to be detested: and though they to You bring nothing whereby they may be saved; “For nothing You shall save them,” that is, with the free gift of Your Grace....
12. “In anger the peoples You shall bring down.” You are angry and dost bring down, dost rage and save, dost terrify and call. Thou fillest with tribulations all things, in order that being set in tribulations men may fly to You, lest by pleasures and a wrong security they be seduced. From You anger is seen, but that of a father. A father is angry with a son, the despiser of his injunctions: being angry with him he boxes him, strikes, pulls the ear, drags with hand, leads to school. How many men have entered, how many men have filled the House of the Lord, in the anger of Him brought down, that is, by tribulations terrified and with faith filled? For to this end tribulation stirs up; in order to empty the vessel which is full of wickedness, so as that it may be filled with grace.
13. “O God, my life I have told out to You”. For that I live has been Your doing, and for this reason I tell out my life to You. But did not God know that which He had given? What is that which you tell out to Him? Will you teach God? Far be it. Therefore why says he, “I have told out to You”? Is it perchance because it profits You that I have told out my life? And what does it profit God? To the advantage of God it does profit. I have told out to God my life, because that life has been God's doing. In like manner as his life Paul the Apostle did tell out, saying, “I that before was a blasphemer and a persecutor and injurious,” he shall tell out his life. “But mercy I have obtained.” He has told out his life, not for himself, but for Him: because he has told it out in such sort, that in Him men believe, not for his own advantages, but for the advantages of Him....“O God, my life I have told out to You. You have put my tears in Your sight.” You have hearkened to me imploring You. “As also in Your promise.” Because as You had promised this thing, so You have done. You have said You would hearken to one weeping. I have believed, I have wept, I have been hearkened unto; I have found You merciful in promising, true in repaying.
14. “Turned be mine enemies backward”. This thing to these very men is profitable, no ill to these men he is wishing. For to go before they are willing, therefore to be amended they are not willing. Thou warnest your enemy to live well, that he amend himself: he scorns, he rejects your word: “Behold him that advises me; behold him from whom I am to hear the commandments whereby I shall live!” To go before you he wills, and in going before is not amended. He minds not that your words are not yours, he minds not that your life to God you tell out, not to yourself. In going before therefore he is not amended: it is a good thing for him that he be turned backward, and follow him whom to go before he willed. The Lord to His disciples was speaking of His Passion that was to be. Peter shuddered, and says, “Far be it, O Lord;” he that a little before had said, “You are the Christ, Son of the living God,” having confessed God, feared for Him to die, as if but a man. But the Lord who so came that He might suffer (for we could not otherwise be saved unless with His blood we were redeemed), a little before had praised the confession of Peter....But immediately when the Lord begins to speak of His Passion, he feared lest He should perish by death, whereas we ourselves should perish unless He died; and he says, “Far be it, O Lord, this thing shall not be done.” And the Lord, to him to whom a little before He had said, “Blessed you are, and upon this Rock I will build my Church,” says, “Go back behind, Satan, an offense you are to Me.” Why therefore “Satan” is he, that a little before was “blessed,” and a “Rock”? “For you savour not the things which are of God,” He says, “but those things which are of man.” A little before he savoured the things which are of God: because “not flesh and blood has revealed to you, but My Father which is in the Heavens.” When in God he was praising his discourse, not Satan but Peter, from petra: but when of himself and out of human infirmity, carnal love of man, which would be for an impediment to his own salvation, and that of the rest, Satan he is called. Why? Because to go before the Lord he willed, and earthly counsel to give to the heavenly Leader. “Far be it, O Lord, this thing shall not be done.” You say, “Far be it,” and you say, “O Lord:” surely if Lord He is, in power He does: if Master He is, He knows what He does, He knows what He teaches. But you will to lead your Leader, teach your Master, command your Lord, choose for God: much you go before, go back behind. Did not this too profit these enemies? “Turned be Mine enemies backward;” but let them not remain backward. For this reason let them be turned backward, lest they go before; but so that they follow, not so that they remain.
15. “In whatsoever day I shall have called upon You, behold I have known that my God are You”. A great knowledge. He says not, “I have known that God You are:” but, “that my God are You.” For yours He is, when you He succours: yours He is, when thou to Him art not an alien. Whence is said, “Blessed the people of whom is the Lord the God of the same.” Wherefore “of whom is”? For of whom is He not? Of all things indeed God He is: but of those men the God peculiarly He is said to be, that love Him, that hold Him, that possess Him, that worship Him, as though belonging to His own House: the great family of Him are they, redeemed by the great blood of the Only Son. How great a thing has God given to us, that His own we should be, and He should be ours! But in truth foreigners afar have been put from holy men, sons alien they are. See what of them is said in another Psalm: “O Lord, deliver me,” he says, “from the hand of alien sons, of whom the mouth has spoken vanity, and the right hand of them is a right hand of iniquity.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)