He was one of our number and shared in this ministry.”
17. Adopted. It is word for word reckoned. And he saith that he was one of the number, that he might signify unto them that it was needful that the empty place should be filled, to the end that the number might continue whole. And to this propose serveth that which followeth, that he had obtained a part in the ministry.
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
For he was numbered with us,.... He was chosen an apostle with: the rest, and was ordained into that office when they were, and was always reckoned one of the twelve, and stands in the catalogue when they are mentioned: and had obtained part of this ministry; by lot, as the word signifies; the providence of God so ordering it, according to his eternal purpose...