2 Do you see how much diligence has been used, that it should be ever borne in mind that He died for us? For since the Marcionists, and Valentinians, and Manichæans were to arise, denying this dispensation, He continually reminds us of the passion even by the mysteries, (so that no man should be deceived); at once saving, and at the same time teaching by means of that sacred table. For this is the chief of the blessings; wherefore Paul also is in every way pressing this.
Then, when He had delivered it, He says, “I will not drink of the fruit of this wine, until that day when I drink it new with you in my Father's kingdom.” For because He had discoursed with them concerning passion and cross, He again introduces what He has to say of His resurrection, having made mention of a kingdom before them, table, and rise up in drunkenness, whereas it were meet to give thanks, and end with an hymn.
Hear this, as many as wait not again for the last prayer of the mysteries, for this is a symbol of that. He gave thanks before He gave it to His disciples, that we also may give thanks. He gave thanks, and sang an hymn after the giving, that we also may do this selfsame thing.
But for what reason does He go forth unto the mountain? Making Himself manifest, that He may be taken, in order not to seem to hide himself. For He hastened to go to the place which was also known to Judas.
Then “He says unto them, All you shall be offended in me.” After this He mentions also a prophecy, “For it is written, I will smite the shepherd, and the sheep shall be scattered abroad:” at once persuading them ever to give heed to the things that are written, and at same time making it plain that He was crucified, according to God's purpose; and by everything showing He was no alien from the old covenant, nor from the God preached therein, but that what is done is a dispensation, and that the prophets all proclaimed all things beforehand from the beginning that are comprised in the matter, so that they be quite confident about the better things also.
And He teaches us to know what the disciples were before the crucifixion, what after the crucifixion. For indeed they who, when He was crucified, were not able so much as to stand their ground, these after His death were mighty, and stronger than adamant.
And this self-same thing is a demonstration of His death, the fright and cowardice, I mean, of His disciples. For if when so many things have been both done and said, still some are shameless, and say that He was not crucified; if none of these things had come to pass, to what pitch of wickedness would they not have proceeded? So for this reason, not by His own sufferings only, but by what took place with respect to the disciples, He confirms the word concerning His death, and by the mysteries also, in every way confounding those that are diseased with the pest of Marcion. For this reason He suffers even the chief apostle to deny Him. But if He was not bound nor crucified, whence sprung the fear to Peter, and to the rest of the apostles.
He suffers them not however, on the other hand, to wait until the sorrows, but what says He? “But after I am risen again, I will go before you into Galilee.” For not from Heaven does He appear at once, neither will He depart into any distant country, but in the same nation, in which He had also been crucified, nearly in the same place, so as hereby again to assure them that He that was crucified was the very same that rose again, and in this way to comfort them more abundantly when in sorrow. Therefore also He said “in Galilee,” that being freed from the fears of the Jews they might believe His saying. For which cause indeed He appeared there.
“But Peter answered and said, Though all men should be offended because of You, yet will I never be offended.”
Source: Homilies on the Gospel of St. Matthew (New Advent)