In those days Peter stood up among the brothers (a gathering of about a hundred and twenty) and said,
15. It was meet that Matthias should be chosen into the place of Judas, lest, through the treachery of one man, all that might seem to have been made of none effect which Christ had once appointed. He did not unadvisedly choose the twelve in the beginning, as principal preachers of his gospel.
The sin of Judas was not only his shame and ruin, but it made a vacancy in the college of the apostles. They were ordained twelve, with an eye to the twelve tribes of Israel, descended from the twelve patriarchs; they were the twelve stars that make up the church's crown (Rev 12:1), and for them twelve thrones were designated, Mat 19:28.
Commenting on Acts 1:15-26
And in those days Peter stood up,.... That is, in one of the days after Christ's ascension, and before the day of Pentecost, whilst the disciples were waiting for the promise of the Spirit. The Ethiopic version reads, "on that day"; as if it was the same day they came first into Jerusalem, and went into the upper room; and which is likely enough; for...