20 “Mine iniquities have taken hold upon me, so that I could not see.” There is a something for us “to see;” what prevents us so that we see it not? Is it not iniquity? From beholding this light your eye is prevented perhaps by some humour penetrating into it; perhaps by smoke, or dust, or by something else that has been thrown into it: and you have not been able to raise your wounded eye to contemplate this light of day. What then? Will you be able to lift up your wounded heart unto God? Must it not be first healed, in order that you may see? Do you not show your pride, when you say, “First let me see, and then I will believe”? Who is there who says this? For who that would fain see, says, “Let me see, and then I will believe”? I am about to manifest the Light unto you; or rather the Light Itself would fain manifest Itself to you! To whom? It cannot manifest Itself to the blind. He does not see. Whence is it that he sees not? It is that the eye is clogged by the multitude of sins....
21. “They are more than the hairs of my head.” He subjects the number of the “hairs of his head” to calculation. Who is there can calculate the number of the hairs of his head? Much less can he tell the number of his sins, which exceed the number of the hairs of his head. They seem to be minute; but they are many in number. You have guarded against great ones; you do not now commit adultery, or murder; you do not plunder the property of others; you do not blaspheme; and do not bear false witness; those are the weightier kind of sins. You have guarded against great sins, what are you doing about your smaller ones? You have cast off the weight; beware lest the sand overwhelm you. “And my heart has forsaken me.” What wonder if your heart is forsaken by your God, when it is even “forsaken” by itself? What is meant by “fails me,” “forsakes me”? Is not capable of knowing itself. He means this: “My heart has forsaken me.” I would fain see God with mine heart, and cannot from the multitude of my sins: that is not enough; mine heart does not even know itself. For no one thoroughly knows himself: let no one presume upon his own state. Was Peter able to comprehend with his own heart the state of his own heart, who said, “I will be with You even unto death”? There was a false presumption in the heart; there was lurking in that heart at the same time a real fear: and the heart was not able to comprehend the state of the heart. Its state was unknown to the sick heart itself: it was manifest to the physician. That which was foretold of him was fulfilled. God knew that in him which he knew not in himself: because his heart had forsaken him, his heart was unknown to his heart.
22. “Be pleased, O Lord, to deliver me”. As if he were saying, “'If You will, You can make me clean.' Be pleased to deliver me. O Lord, look upon me to help me.” Look, that is, on the penitent members, members that lie in pain, members that are writhing under the instruments of the surgeon; but still in hope.
23. “Let them be ashamed and confounded together that seek after my soul to destroy it”. For in a certain passage he makes an accusation, and says, “I looked upon my right hand, and beheld; and there was no man who sought after my soul;” that is, there was no man to imitate Mine example. Christ in His Passion is the Speaker. “I looked on my right hand,” that is, not on the ungodly Jews, but on My own right hand, the Apostles,— “and there was no man who sought after My soul.” So thoroughly was there no man to “seek after My soul,” that he who had presumed on his own strength, “denied My soul.” But because a man's soul is sought after in two ways, either in order that you may enjoy his society; or that you may persecute him; therefore he here speaks of others, whom he would have “confounded and ashamed,” who are “seeking after his soul.” But lest you should understand it in the same way as when he complains of some who did not “seek after his soul,” He adds, “to destroy it;” that is, they seek after my soul in order to my death....
24. “Let them be turned backward and put to shame that wish me evil.” “Turned backwards.” Let us not take this in a bad sense. He wishes them well; and it is His voice, who said from the Cross, “Father, forgive them; for they know not what they do.” Wherefore then does he say to them, that they should return “backwards”? Because they who before were proud, so that they fell, are now become humble, so that they may rise again. For when they are before, they are wishing to take precedence of their Lord; to be better than He; but if they go behind Him, they acknowledge Him to be better than they; they acknowledge that He ought to go before; that He should precede, they follow. Thence He thus rebukes Peter giving Him evil counsel. For the Lord, when about to suffer for our salvation, also foretold what was to happen concerning that Passion itself; and Peter says, “Be it far from You,” “God forbid it!” “This shall not be!” He would fain have gone before his Lord; would have given counsel to his Master! But the Lord, that He might make him not go before Him, but follow after Him, says, “Get behind, Satan!” It is for this reason He said “Satan,” because you are seeking to go before Him, whom you ought to follow; but if you are behind, if you follow Him, you will henceforth not be “Satan.” What then? “Upon this Rock I will build My Church.”...
25. “Let them speedily bear away their own confusion, that say unto me, Well done! Well done!”. They praise you without reason. “A great man! A good man! A man of education and of learning; but why a Christian?” They praise those things in you which you should wish not to be praised; they find fault with that at which you rejoice. But if perhaps you say, “What is it you praise in me, O man? That I am a virtuous man? A just man? If you think this, Christ made me this; praise Him.” But the other says, “Be it far from you. Do yourself no wrong! You yourself made yourself such.” “Let them be confounded who say unto me, Well done! Well done!” And what follows?
“Let all those that seek You, O Lord, rejoice and be glad”. Those who “seek” not me, but “You;” who say not to me, “Well done! Well done!” but see me “glory in You,” if I have anything whereof to glory; for “he who glories, let him glory in the Lord.” “Let all those who seek You, Lord, rejoice and be glad.”
“And say continually, the Lord be magnified.” For even if the sinner becomes righteous, you should give the glory to “Him who justifies the ungodly.” Whether therefore it be a sinner, let Him be praised who calls him to forgiveness; or one already walking in the way of righteousness, let Him be praised who calls him to receive the crown! Let the Name of the Lord be magnified continually by “such as love Your salvation.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)