3 What do you say, O Peter? The prophet said, “The sheep shall be scattered;” Christ has confirmed the saying, and do you say, No? Is not what passed before enough, when Thou said, “Far be it from You,” and your mouth was stopped? For this then He suffers him to fall, teaching him thereby to believe Christ in all things, and to account His declaration more trustworthy than one's own conscience. And the rest too reaped no small benefit from his denial, having come to know man's weakness, and God?' s truth. For when He foretells anything, we must no longer be subtle, nor lift up ourselves above the common sort. For, “your rejoicing,” it is said, “you shall have in yourself, and not in another.” For where he should have prayed, and have said, Help us, that we be not cut off, he is confident in himself, and says, “Though all men should be offended in You, yet will I never;” though all should undergo this, I shall not undergo it, which led him on little by little to self-confidence. Christ then, out of a desire to put down this, permitted his denial. For since he neither submitted to Him nor the prophet (and yet for this intent He brought in the prophet besides, that they may not gainsay), but nevertheless since he submitted not to His words, he is instructed by deeds.
For in proof that for this intent He permitted it, that He might amend this in him, hear what He says, “I have prayed for you, that your faith fail not.” For this He said sharply reproving him, and showing that his fall was more grievous than the rest, and needed more help. For the matters of blame were two; both that he gainsaid; and, that he set himself before the other; or rather a third too, namely, that he attributed all to himself.
To cure these things then, He suffered the fall to take place, and for this cause also leaves the others, and addresses Himself earnestly to him. For, “Simon,” says He, “Simon, behold Satan has desired to have you that he may sift you as wheat;” that is, that he may trouble, confound, tempt you; but “I have prayed for you, that your faith fail not.”
And why, if Satan desired all, did He not say concerning all, I have prayed for you? Is it not quite plain that it is this, which I have mentioned before, that it is as reproving him, and showing that his fall was more grievous than the rest, that He directs His words to him?
And wherefore said He not, But I did not suffer it, rather than, “I have prayed?” He speaks from this time lowly things, on His way to His passion, that He may show His humanity. For He that has built His church upon Peter's confession, and has so fortified it, that ten thousand dangers and deaths are not to prevail over it; He that has given him the keys of Heaven, and has put him in possession of so much authority, and in no manner needed a prayer for these ends (for neither did He say, I have prayed, but with His own authority, “I will build my church, and I will give you the keys of Heaven”), how should He need to pray, that He might brace up the shaken soul of a single man? Wherefore then did He speak in this way? For the cause which I mentioned, and because of their weakness, for they had not as yet the becoming view of Him.
How then was it that He denied? He said not, that you may not deny, but that your faith fail not, that you perish not utterly. For this came from His care.
For indeed fear had driven out all else, for it was beyond measure, and it became beyond measure, since God had to an exceeding degree deprived him of His help, and He did exceedingly deprive him thereof, because there was to an exceeding degree in him the passion of self-will and contradiction. In order then that He might pluck it up by the roots, therefore He suffered the terror to overtake him.
For in proof that this passion was grievous in him, he was not content with his former words, gainsaying both prophet and Christ, but also after these things when Christ had said unto him, “Verily I say unto you, that this night, before the cock crow, you shall deny me thrice,” he replies, “Though I should die with You, I will not deny You in any wise.” And Luke signifies moreover, that the more Christ warned him, so much the more did Peter exceedingly oppose Him.
What mean these things, O Peter? When He was saying, “One of you shall betray me,” you feared lest you should be the traitor, and constrained the disciple to ask, although conscious to yourself of no such thing; but now, when He is plainly crying out, and saying, “All shall be offended,” are you gainsaying it, and not once only, but twice and often? For this is what Luke says.
Whence then did this come to him? From much love, from much pleasure. I mean, that after that he was delivered from that distressing fear about the betrayal, and knew the traitor, he then spoke confidently, and lifted himself up over the rest, saying, “Though all men shall be offended, yet will I not be offended.” And in some degree too his conduct sprung from jealousy, for at supper they reasoned “which of them is the greater,” to such a degree did this passion trouble them. Therefore He checked him, not compelling him to the denial, God forbid! But leaving him destitute of His help, and convicting human nature.
See at any rate after these things how he was subdued. For after the resurrection, when he had said, “And what shall this man do?” and was silenced, he ventured no more to gainsay as here, but held his peace. Again, towards the assumption, when he heard, “It is not for you to know times or seasons,” again he holds his peace, and contradicts not. After these things, on the house, and by the sheet, when he heard a voice saying to him, “What God has cleansed, call not thou common,” even though he knew not for the time what the saying could be, he is quiet, and strives not.
Source: Homilies on the Gospel of St. Matthew (New Advent)