Matthew Henry Commentary Acts 1:15-26

"And in these days Peter stood up in the midst of the brethren, and said (and there was a multitude of persons [gathered] together, about a hundred and twenty), Brethren, it was needful that the Scripture should be fulfilled, which the Holy Spirit spake before by the mouth of David concerning Judas, who was guide to them that took Jesus. For he was numbered among us, and received his portion in this ministry. (Now this man obtained a field with the reward of his iniquity; and falling headlong, he burst asunder in the midst, and all his bowels gushed out. And it became known to all the dwellers at Jerusalem; insomuch that in their language that field was called Akeldama, that is, The field of blood.) For it is written in the book of Psalms, Let his habitation be made desolate, And let no man dwell therein: and, His office let another take. Of the men therefore that have companied with us all the time that the Lord Jesus went in and went out among us, beginning from the baptism of John, unto the day that he was received up from us, of these must one become a witness with us of his resurrection. And they put forward two, Joseph called Barsabbas, who was surnamed Justus, and Matthias. And they prayed, and said, Thou, Lord, who knowest the hearts of all men, show of these two the one whom thou hast chosen, to take the place in this ministry and apostleship from which Judas fell away, that he might go to his own place. And they gave lots for them; and the lot fell upon Matthias; and he was numbered with the eleven apostles." — Acts 1:15-26 (ASV)

The great thing the apostles were to attest to the world was Christ's resurrection, for that was the great proof of His being the Messiah and the foundation of our hope in Him. The apostles were ordained, not to worldly dignity and dominion, but to preach Christ and the power of His resurrection.

An appeal was made to God: “You, Lord, who know the hearts of all men,” which we do not; and He knows them even better than they know their own. It is fitting that God should choose His own servants; and insofar as He, by the workings of His providence or the gifts of His Spirit, shows whom He has chosen, or what He has chosen for us, we ought to submit to His will. Let us acknowledge His hand in determining everything that befalls us, especially in those matters by which any trust may be committed to us.