13 Let then our Head say, “False witnesses did rise up, they laid to My charge things that I knew not”. But let us say to our Head, Lord, what knew Thou not? Did Thou indeed know not anything? Did You not know the hearts of them that charged You? Did You not foresee their deceits? Did You not give Yourself into their hands knowingly? Had You not come that You might suffer by them? What then knew Thou not? He knew not sin, and thereby He knew not sin, not by not judging, but by not committing. There are phrases of this kind also in daily use, as when you say of any one, He knows not to stand, that is, he does not stand; and, He knows not to do good, because he does not good; and, He knows not to do ill, because he does not ill....What knew not Christ so much, as to blaspheme? Thereof was He called in question by His persecutors, and because He spoke truth, He was judged to have spoken blasphemy. But by whom? By them of whom it follows, “They rewarded Me evil for good, and barrenness to My Soul”. I gave unto them fruitfulness, they rewarded Me barrenness; I gave life, they death; I honour, they dishonour; I medicine, they wounds; and in all these which they rewarded Me, was truly barrenness. This barrenness in the tree He cursed, when seeking fruit He found none. Leaves there were, and fruit there was not: words there were, and deeds there were not. See of words abundance, and of deeds barrenness. “Thou that preachest a man should not steal, stealest: thou that sayest a man should not commit adultery, committest adultery.” Such were they who charged Christ with things that He knew not.
14. “But I, when they troubled me, clothed myself with sackcloth, and humbled my soul with fasting, and my prayer shall return into my own bosom”...Brethren, if for some little space with pious curiosity we lift the veil, and search with the intent eye of the heart the inner part of this Scripture, we find that even this the Lord did. Sackcloth, haply He calls His mortal flesh. Wherefore Sackcloth? For the likeness of sinful flesh. For the Apostle says, “God sent His Son in the likeness of sinful flesh, that through sin He might condemn sin in the flesh:” that is, He clothed His Own Son with sackcloth, that through sackcloth He might condemn the goats. Not that there was sin, I say not in the Word of God, but not even in that Holy Soul and Mind of a Man, which the Word and Wisdom of God had so joined to Himself as to be One Person. Nay, nor even in His very Body was any sin, but the likeness of sinful flesh there was in the Lord; because death is not but by sin, and surely that Body was mortal. For had It not been mortal, It had not died; had It not died, It had not risen again; had It not risen again, It had not showed us an example of eternal life. So then death, which is caused by sin, is called sin; as we say the Greek tongue, the Latin tongue, meaning not the very member of flesh, but that which is done by the member of flesh. For the tongue in our members is one among others, as the eyes, nose, ears, and the rest: but the Greek tongue is Greek words, not that the tongue is words, but that words are by the tongue....So then the sin of the Lord is that which was caused by sin; because He assumed flesh, of the same lump which had deserved death by sin. For to speak more briefly, Mary who was of Adam died for sin, Adam died for sin, and the Flesh of the Lord which was of Mary died to put away sin. With this sackcloth the Lord clothed Himself, and therefore was He not known, because He lay hid under sackcloth. “When they,” says He, “troubled Me, I clothed Myself with sackcloth:” that is, they raged, I lay hid. For had He not willed to lie hidden neither could He have died, since in one moment of time one drop only of His Power, if indeed it is to be called a drop, He put forth, when they wished to seize Him, and at His one question, “Whom do you seek?” they all went back and fell to the ground. Such power could He not have humbled in passion, if He had not lain hid under sackcloth.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)