16 Men and brethren, this scripture must needs have been fulfilled, which the Holy Ghost by the mouth of David spake before concerning Judas, which was guide to them that took Jesus.
The Apostle Peter, therefore, after the resurrection of the Lord, and His assumption into the heavens, being desirous of filling up the number of the twelve apostles, and in electing into the place of Judas any substitute who should be chosen by God, thus addressed those who were present: "Men [and] brethren, this Scripture must needs have been fulfilled, which the Holy Ghost, by the mouth of David, spoke before concerning Judas, which was made guide to them that took Jesus. For he was numbered with us: [Acts 1:16, etc.] ... Let his habitation be desolate, and let no man dwell therein; and, His bishoprick let another take;" — thus leading to the completion of the apostles, according to the words spoken by David.
Accordingly, after one of these had been struck off, He commanded the eleven others, on His departure to the Father, to “go and teach all nations, who were to be baptized into the Father, and into the Son, and into the Holy Ghost.” [Matt. 28:19] Immediately, therefore, so did the apostles, whom this designation indicates as “the sent.” Having, on the authority of a prophecy, which occurs in a psalm of David, [Ps. 109:8] chosen Matthias by lot as the twelfth [Acts 1:15-20], into the place of Judas, they obtained the promised power of the Holy Ghost for the gift of miracles and of utterance; and after first bearing witness to the faith in Jesus Christ throughout Judæa, and founding churches (there), they next went forth into the world and preached the same doctrine of the same faith to the nations. They then in like manner founded churches in every city, from which all the other churches, one after another, derived the tradition of the faith, and the seeds of doctrine, and are every day deriving them, that they may become churches. Indeed, it is on this account only that they will be able to deem themselves apostolic, as being the offspring of apostolic churches.
"Men and brethren," he says, "this Scripture must needs have been fulfilled, which the Holy Ghost spake before." Why did he not ask Christ to give him some one in the room of Judas? It is better as it is. For in the first place, they were engaged in other things; secondly, of Christ's presence with them, the greatest proof that could be given was this: as He had chosen when He was among them, so did He now being absent. Now this was no small matter for their consolation. But observe how Peter does everything with the common consent; nothing imperiously. And he does not speak thus without a meaning. But observe how he consoles them concerning what had passed. In fact, what had happened had caused them no small consternation. For if there are many now who canvass this circumstance, what may we suppose they had to say then?
"This Scripture," says he, "must needs have been fulfilled, which the Holy Ghost spake before." Always he comforts them by the prophecies. So does Christ on all occasions. In the very same way, he shows here that no strange thing had happened, but what had already been foretold. "This Scripture must needs have been fulfilled," he says, which the Holy Ghost by the mouth of David spake before." He does not say, David, but the Spirit through him. See what kind of doctrine the writer has at the very outset of the book. Do you see, that it was not for nothing that I said in the beginning of this work, that this book is the Polity of the Holy Spirit? "Which the Holy Ghost spake before by the mouth of David." Observe how he appropriates him; and that it is an advantage to them, that this was spoken by David, and not by some other Prophet.
Here is forethought for providing a teacher; here was the first who ordained a teacher. He did not say, "We are sufficient." So far was he beyond all vain-glory, and he looked to one thing alone. And yet he had the same power to ordain as they all collectively. But well might these things be done in this fashion, through the noble spirit of the man, and because prelacy then was not an affair of dignity, but of provident care for the governed.
Twelve constellations of the [stellar] choir shine and cast the brilliance of Olympus on the earth. Note what realization this light reveals: The world is divided by the regions of its four sides; a triune faith calls this [world to belief], in whose name [the world] is washed in the font. Therefore, four taken together three times makes up the whole figure which the twelvefold order possesses, and to the devout disciples, to whom this baptism is commanded, a mystic reason gave cause for making up again the former number.
Brethren, it is necessary to fulfill the Scripture which the Holy Spirit foretold, etc. Peter the Apostle feared to remain in the number eleven. For all sin is 'eleven,' because through perverse actions, it transgresses the precepts of the Decalogue. Hence, because none of our justice is innocent by itself, the tabernacle that contained the Ark of the Lord was overlaid inside with eleven goat-hair curtains. And he restored the number of apostles to twelve, so that by the two parts of seven (for three times four is a fine sum), they would maintain the grace they preached and with the number, and those who were to preach the faith of the Holy Trinity to the fourfold world, as the Lord says: "Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit" (Matthew 28:19), they would also strengthen the perfection of work by the sacrament of the number. According to the higher understanding, the loss that the Church suffers from false brethren persists to the greatest extent unaddressed. But when at the end of the world, the people of the Jews who crucified the Lord are believed to be reconciled to the Church, like on the approaching fiftieth day, the number of the apostles is restored.
the scripture had to be fulfilled: Not that scripture forced the event, but it did mention an event that would happen: This scripture says: He who ate my bread has lifted his heel against me.(Psalm 41:9)
who was the leader of those who apprehended Jesus: Judas had agreed with the chief priests to betray Christ, he looked for an opportunity to deliver him without disturbing the people. And because some of the crowd might resist, he took a band of soldiers, not from the Jews, but from the governor. In this way, no one would dare to resist because they would see the marks of legitimate authority. Further, some Jews might resist out of zeal for the law, especially because Christ was being taken by Gentiles. For this reason Judas took some servants or officers from the chief priests and the Pharisees. (John 18:3)
[AD 202] Irenaeus on Acts 1:16