Note 9 at Ac 18:10: Paul already had a good idea of how many Christians there were in Corinth; he was the one who had introduced the Gospel of Jesus to them. Therefore, this must be speaking of others who were not yet Christians but yet were God's people.

God, in His foreknowledge (see note 4 at Joh 13:5), knew those who would accept the Gospel if given the opportunity, and this must have been the group He was referring to. He urged Paul to stay and continue to preach the good news till all those who were ordained to eternal life believed (Ac 13:48).