A.T. Robertson Commentary Acts 20:3

"And when he had spent three months [there,] and a plot was laid against him by Jews as he was about to set sail for Syria, he determined to return through Macedonia." — Acts 20:3 (ASV)

When he had spent three months there (ποιησας μηνας τρεις). Literally, "having done three months," the same idiom in Ac 14:33; 18:23; James 5:13. During this period Paul may have written Galatians as Lightfoot argued and certainly did Romans. We do not have to say that Luke was ignorant of Paul's work during this period, only that he did not choose to enlarge upon it.

And a plot was laid against him by the Jews (γενομενης επιβουλης αυτω υπο των Ιουδαιων). Genitive absolute, "a plot by the Jews having come against him." Επιβουλη is an old word for a plot against one. In the N.T. only in Acts (9:24; 20:3,19; 23:30). Please note that this plot is by the Jews, not the Judaizers whom Paul discusses so vehemently in 2Colossians 10-13. They had given Paul much anguish of heart as is shown in I Cor. and in 2Colossians 1-7, but that trouble seems now past. It is Paul's old enemies in Corinth who had cherished all these years their defeat at the hands of Gallio (Acts 18:5–17) who now took advantage of Paul's plans for departure to compass his death if possible.

As he was about to set sail for Syria (μελλοντ αναγεσθα εις την Συριαν). The participle μελλοντ agrees in case (dative) with αυτω. For the sense of intending see also verse 13. Αναγεσθα (present middle infinitive) is the common word for putting out to sea (going up, they said, from land) as in 13:13.

He determined (εγενετο γνωμης). The best MSS. here read γνωμης (predicate ablative of source like επιλυσεως, 2 Peter 1:20, Robertson, Grammar, p. 514), not γνωμη (nominative). "He became of opinion." The Jews had heard of Paul's plan to sail for Syria and intended in the hurly-burly either to kill him at the docks in Cenchreae or to push him overboard from the crowded pilgrim ship bound for the passover. Fortunately Paul learned of their plot and so eluded them by going through Macedonia. The Codex Bezae adds here that "the Spirit bade him return into Macedonia."