(Verse 15) - In those days - On one of the days intervening between the ascension of Jesus and the day of Pentecost.

Peter stood up - Peter standing up, or rising. This is a customary expression in the Scriptures when one begins to do a thing, (Luke 15:18). The reason why Peter did this may be seen in Matt. 16:16-17. It is not improbable, besides, that Peter was the most aged of the apostles; and from his uniform conduct we know that he was the most ardent. It was perfectly characteristic, therefore, for him to introduce the business of the election of a new apostle.

The disciples - This was the name, which was given to them as being learners in the school of Christ. (See Matt. 5:1).

The number of the names - The number of the persons, or individuals. The word “name” is often used to denote “the person,” (Rev. 3:4; Acts 4:12; 18:15; Eph. 1:21).  This was the first assembly convened to transact the business of the church; and it is not a little remarkable that the vote in so important a matter as electing apostle was by the entire church. It settles the question that the election of a minister and pastor should be by the church, and that a pastor should not be placed over a church by a patron, or by a denomination. If a case could ever occur where it would be right and proper that one should be selected to exercise the office of a minister of Christ by the ministry only, the election of one to fall the office of an apostle was such a case. And yet in this the entire church had a voice.

Whether this was all the true church at this time does not appear from the history. This expression cannot mean that there were no more Christians, but that these were all that had convened in the upper room. It is certain that our Savior had, by his own ministry, brought many others to be his true followers. (Cp. 1 Cor. 15:6).

(Verse 16) - Men and brethren - This is a customary mode of address, implying affection and respect, (Acts 13:26). Another vesion renders it more appropriately than by the introduction of the conjunction “and” - “Men, our brethren.”

This scripture - This prediction contained in the writings of the Old Testament. (Cp. John 5:39). The passage to which Peter refers is commonly supposed to be that recorded in Ps. 41:9, “Yea, mine own familiar friend hath lifted up his heel against me.” This is expressly applied to Judas by our Savior, in John 13:18. But it seems clear that the reference is not to the 41st Psalm, but to the passage in the 69th Psalm which Peter proceeds to quote in Acts 1:20.

Must needs have been fulfilled - It would certainly be fulfilled. Not that there was any physical necessity or any compulsion; but it could not but occur that a prediction of God would be fulfilled. This makes no affirmation about the freedom of Judas in doing it. A man will be just as free in wickedness if it be foretold that he will be wicked, as if it had never been known to any other being but himself.

The Holy Ghost  - This is a strong attestation to the inspiration of David, and accords with the uniform testimony of the New Testament, that the sacred writers spake as they were moved by the Holy Spirit, (2 Pet. 1:21).

Concerning Judas - In what respect this was concerning Judas, see Acts 1:20.

Which was guide  - (Matt. 26:47; John 18:3).