while Apollos was at Corinth - where his ministry was so powerful that a formidable party in the Church of that city gloried in his type of preaching in preference to Paul’s (1Co 1:12; 1Co 3:4), no doubt from the marked infusion of Greek philosophic culture which distinguished it, and which the apostle studiously avoided (1Co 2:1-5).
Paul having passed through the upper coasts - “parts,” the interior of Asia Minor, which, with reference to the seacoast, was elevated.
came to Ephesus - thus fulfilling his promise (Act 18:21).
finding certain disciples - in the same stage of Christian knowledge as Apollos at first, newly arrived, probably, and having had no communication as yet with the church at Ephesus.