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 the notes on Matthew 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 the notes on Matthew 5:1.
The number of the names - The number of the persons, or individuals. The word “name” is often used to denote “the person,” Revelation 3:4; Acts 4:12; Acts 18:15; Ephesians 1:21. In Syriac it is, “The assembly of people was about an hundred and twenty.” 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 an ecclesiastical body. 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 Saviour had, by his own ministry, brought many others to be his true followers. Compare 1 Corinthians 15:6.