“And some days after Paul said unto Barnabas, Let us go again and visit our brethren in every city where we have preached the word of the Lord, and see how they do. And Barnabas determined to take with them John, whose surname was Mark. But Paul thought not good to take him with them, who departed from them from Pamphylia, and went not with them to the work. And the contention was so sharp between them, that they departed asunder one from the other: and so Barnabas took Mark, and sailed unto Cyprus; And Paul chose Silas, and departed . . .” (Acts 15:36-40).
I know Paul thought he was right. Mark had abandoned them in Perga (see Acts 13:13). We do not know the reason, and in this context it doesn't really matter. Differences of opinion are acceptable. Contention is not. Paul, in his zeal, seems determined not to keep company with one less zealous than he was. That is all right. But the contention is not. We know where that comes from and how damaging it can be to missionary work.