4 For now the Person of the Lord begins to appear speaking in this Psalm. For it follows, “I will sing to Your Name, O Most High, in turning mine enemy behind.” His enemy then, where was he turned back? Was it when it was said to him, “Get behind, Satan”? For then he who by tempting desired to put himself before, was turned behind, by failing in deceiving Him who was tempted, and by availing nothing against Him. For earthly men are behind: but the heavenly man is preferred before, although he came after. For “the first man is of the earth, earthy: the second Man is from heaven, heavenly.” But from this stock he came by whom it was said, “He who comes after me is preferred before me.” And the Apostle forgets “those things that are behind, and reaches forth unto those things that are before.” The enemy, therefore, was turned behind, after that he could not deceive the heavenly Man being tempted; and he turned himself to earthy men, where he can have dominion....For in truth the devil is turned behind, even in the persecution of the righteous, and he, much more to their advantage, is a persecutor, than if he went before as a leader and a prince. We must sing then to the Name of the Most High in turning the enemy behind: since we ought to choose rather to fly from him as a persecutor, than to follow him as a leader. For we have whither we may fly and hide ourselves in the hidden things of the Son; seeing that “the Lord has been made a refuge for us.”
5. “They will be weakened, and perish from Your face”. Who will be weakened and perish, but the unrighteous and ungodly? “They will be weakened,” while they shall avail nothing; “and they shall perish,” because the ungodly will not be; “from the face” of God, that is, from the knowledge of God, as he perished who said, “But now I live not, but Christ lives in me.” But why will the ungodly “be weakened and perish from your face?” “Because,” he says, “You have made my judgment, and my cause:” that is, the judgment in which I seemed to be judged, You have made mine; and the cause in which men condemned me just and innocent, You have made mine. For such things served Him for our deliverance: as sailors too call the wind theirs, which they take advantage of for prosperous sailing.
6. “You sat on the throne Who judgest equity”. Whether the Son say this to the Father, who said also, “You could have no power against Me, except it were given you from above,” referring this very thing, that the Judge of men was judged for men's advantage, to the Father's equity and His own hidden things: or whether man say to God, “You sat on the throne Who judgest equity,” giving the name of God's throne to his soul, so that his body may perhaps be the earth, which is called God's “footstool:” for “God was in Christ, reconciling the world unto Himself:” or whether the soul of the Church, perfect now and without spot and wrinkle, worthy, that is, of the hidden things of the Son, in that “the King has brought her into His chamber,” say to her spouse, “You sat upon the throne Who judgest equity,” in that You have risen from the dead, and ascended up into heaven, and sittest at the right hand of the Father: whichsoever, I say, of those opinions, whereunto this verse may be referred, is preferred, it transgresses not the rule of faith.
7. “You have rebuked the heathen, and the ungodly has perished”. We take this to be more suitably said to the Lord Jesus Christ, than said by Him. For who else has rebuked the heathen, and the ungodly perished, save He, who after that He ascended up into heaven, sent the Holy Ghost, that, filled by Him, the Apostles should preach the word of God with boldness, and freely reprove men's sins? At which rebuke the ungodly perished; because the ungodly was justified and was made godly. You have effaced their name for the world, and for the world's world. The name of the ungodly has been effaced. For they are not called ungodly who believe in the true God. Now their name is effaced “for the world,” that is, as long as the course of the temporal world endures. “And for the world's world.” What is “the world's world,” but that whose image and shadow, as it were, this world possesses? For the change of seasons succeeding one another, while the moon is on the wane, and again on the increase, while the sun each year returns to his quarter, while spring, or summer, or autumn, or winter passes away only to return, is in some sort an imitation of eternity. But this world's world is that which abides in immutable eternity. As a verse in the mind, and a verse in the voice, the former is understood, the latter heard; and the former fashions the latter; and hence the former works in art and abides, the latter sounds in the air and passes away. So the fashion of this changeable world is defined by that world unchangeable which is called the world's world. And hence the one abides in the art, that is, in the Wisdom and Power of God: but the other is made to pass in the governance of creation. If after all it be not a repetition, so that after it was said “for the world,” lest it should be understood of this world that passes away, it were added “for the world's world.” For in the Greek copies it is thus, εἰς τὸν αἰῶνα, καὶ εἰς τὸν αἰῶνα τοῦ αἰῶνος Which the Latins have for the most rendered, not, “for the world, and for the world's world;” but, “for ever, and for the world's world,” that in the words “for the world's world.” the, words “for ever,” should be explained. “The name,” then, “of the ungodly You have effaced for ever,” for from henceforth the ungodly shall never be. And if their name be not prolonged unto this world, much less unto the world's world.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)