But Paul thought not good to take [Mark] with them, who . . . went not with them to the work.
Paul and Barnabas had made a great team in the gospel work. But at this point they had a violent disagreement over John Mark, and parted company. Paul’s concern was that John Mark had started out with them on their missionary journey but at one point had turned back and returned to Jerusalem. We aren’t told why, but it seems that Paul didn’t think it wise to take Mark again, until he proved himself. Young believer, don’t turn back. There are many disappointed people when they see one turn back, not to mention the disappointment that the Lord feels. Keep your hand to the plough. Don’t turn back!