“For he was numbered with us,” (πρὥτος τοῦ πράγματος αὐθεντει absent from A.B.C) says Peter. On this account it behooves to propose another; to be a witness in his place. And see how he imitates his Master, ever discoursing from the Scriptures, and saying nothing as yet concerning Christ; namely, that He had frequently predicted this Himself. Nor does he mention where the Scripture speaks of the treachery of Judas; for instance, “The mouth of the wicked and the mouth of the deceitful are opened against me”; but where it speaks only of his punishment; for this was most to their advantage. It shows again the benevolence of the Lord: “For he was numbered with us” (τοὕτο γὰρ αὐτοὺς μάλιστα ὡφέλει· Δείκνυσι πάλιν A.B.C), he says, “and obtained his lot of this ministry.” He calls it everywhere “lot,” showing that the whole is from God's grace and election, and reminding them of the old times, inasmuch as God chose him into His own lot or portion, as of old He took the Levites. He also dwells upon the circumstances respecting Judas, showing that the reward of the treachery was made itself the herald of the punishment. For he “acquired,” he says, “a field out of the reward of the iniquity.” Observe the divine economy in the event. “Of the iniquity,” he says. For there are many iniquities, but never was anything more iniquitous than this: so that the affair was one of iniquity. Now not only to those who were present did the event become known, but to all thereafter, so that without meaning or knowing what they were about, they gave it a name; just as Caiaphas had prophesied unconsciously. God compelled them to call the field in Hebrew “Aceldama.” By this also the evils which were to come upon the Jews were declared: and Peter shows the prophecy to have been so far in part fulfilled, which says, “It had been good for that man if he had not been born.” We may with propriety apply this same to the Jews likewise; for if he who was guide suffered thus, much more they. Thus far however Peter says nothing of this. Then, showing that the term, “Aceldama,” might well be applied to his fate, he introduces the prophet, saying, “Let his habitation be desolate.” For what can be worse desolation than to become a place of burial? And the field may well be called his. For he who cast down the price, although others were the buyers, has a right to be himself reckoned owner of a great desolation. This desolation was the prelude to that of the Jews, as will appear on looking closely into the facts. For indeed they destroyed themselves by famine, and killed many, and the city became a burial-place of strangers, of soldiers, for as to those, they would not even have let them be buried, for in fact they were not deemed worthy of sepulture.
“Wherefore of these men which have companied with us,” continues Peter. Observe how desirous he is they should be eye-witnesses. It is true indeed that the Spirit would shortly come; and yet great care is shown with regard to this circumstance. “Of these men,” he says, “which have companied with us, all the time that the Lord Jesus went in and out among us.” He shows that they had dwelt with Christ, not simply been present as disciples. In fact, from the very beginning there were many that then followed Him. Observe, for instance, how this appears in these words: “One of the two which heard John speak, and followed Jesus.— All the time,” he says, “that the Lord Jesus went in and out among us, beginning from the baptism of John.” True! For no one knew what preceded that event, though they did learn it by the Spirit. “Unto that same day that He was taken up from us, must one be ordained to be a witness with us of His resurrection.” He said not, a witness of the rest of his actions, but a witness of the resurrection alone. For indeed that witness had a better right to be believed, who was able to declare, that He Who ate and drank, and was crucified, the same rose again. Wherefore it was needed that he should be a witness, not only of the time preceding this event, nor only of what followed it, and of the miracles; the thing required was, the resurrection. For the other matters were manifest and acknowledged, but the resurrection took place in secret, and was manifest to these only. And they do not say, Angels have told us; but, We have seen. For this it was that was most needful at that time: that they should be men having a right to be believed, because they had seen.
“And they appointed two,” it is said. Why not many? That the feeling of disappointment might not reach further, extending to many. Again, it is not without reason that he puts Matthias last; he would show, that frequently he that is honourable among men, is inferior before God. And they all pray in common saying, “You, Lord, which know the hearts of all men, show. You,” not “We.” And very seasonably they use the epithet, “heart-knowing:” for by Him Who is this must the choice be made. So confident were they, that assuredly one of them must be appointed. They said not, Choose, but, “Show the chosen one;” knowing that all things were foreordained of God; “Whom You chose: one of these two,” say they, “to have his lot in this ministry and apostleship.” For there was besides another ministry (διακονία). “And they gave them their lots.” For they did not yet consider themselves to be worthy to be informed by some sign. And besides, if in a case where neither prayer was made, nor men of worth were the agents, the casting of lots so much availed, because it was done of a right intention, I mean in the case of Jonah; much more did it here. Thus, did he, the designated, fill up the company, complete the order: but the other candidate was not annoyed; for the apostolic writers would not have concealed [that or any other] failings of their own, seeing they have told of the very chief Apostles, that on other occasions they had indignation, and this not once only, but again and again.
Source: Homilies on Acts (New Advent)