A.T. Robertson Commentary Acts 18:21

"but taking his leave of them, and saying, I will return again unto you if God will, he set sail from Ephesus." — Acts 18:21 (ASV)

I shall return (ανακαμψω). Future active indicative of ανακαμπτω, old verb to bend back, turn back (Matthew 2:2).

If God will (του θεου θελοντος). Genitive absolute of present active participle. This expression (εαν with subjunctive) occurs also in 1 Corinthians 4:19; 16:7; James 4:15. Such phrases were common among Jews, Greeks, and Romans, and are today. It is simply a recognition that we are in God's hands. The Textus Receptus has here a sentence not in the best MSS.: "I must by all means keep this feast that cometh in Jerusalem." This addition by D and other documents may have been due to a desire to give a reason for the language in verse 22 about "going up" to Jerusalem. Whether Paul said it or not, it was in the spring when he made this journey with a company of pilgrims probably going to the feast of Pentecost in Jerusalem. We know that later Paul did try to reach Jerusalem for Pentecost (20:16) and succeeded. As the ship was leaving, Paul had to go, but with the hope of returning soon to Ephesus as he did.