Paula

I see an important issue with the choosing of Matthias as what Peter said in vs. 21-22, that it had to be someone who was with them from John’s baptism to Jesus’ ascension. Paul could not possibly qualify for that. And this was all Peter’s doing, not the group’s. Then they first prayed for God to direct the choice between two proposed candidates, and only then cast the lot. Lot casting of course was a legitimate method of finding the will of God in OT times, and at this early stage there was no other method, as the Holy Spirit had not yet come.

Paul, per his own words, was the apostle to the Gentiles, whereas the 12 were to the Jews. And he was uniquely commissioned to reveal the mystery, that is, the unity of Jew and Gentile into one Body. So his mission was entirely different from that of the 12.