"Then after some days Paul said to Barnabas, 'Let us now go back and visit our brethren in every city where we have preached the word of the Lord, and see how they are doing.' Now Barnabas was determined to take with them John called Mark. But Paul insisted that they should not take with them the one who had departed from them in Pamphylia, and had not gone with them to the work. Then the contention became so sharp that they parted from one another. And so Barnabas took Mark and sailed to Cyprus; but Paul chose Silas and departed, being commended by the brethren to the grace of God. And he went through Syria and Cilicia, strengthening the churches" (Acts 15:36-41).
Although we don't know for certain how long Paul and Barnabas stayed in Antioch after returning from their first evangelistic journey to Cyprus, Pamphylia, and Pisidia, it was likely many months. These godly men were very conscientious about those they had taught and helped obey the gospel of Christ. They wanted to see how the new Christians were doing and strengthen them in the faith. It is important to continue to teach new Christians after their conversion (cf. I Pet. 2:2; Matt. 28:20). They could communicate via written letters (and Paul did do this often, as his many New Testament epistles illustrate), but such would not be nearly as effective for helping growing Christians as a personal visit. Such is still true today. In our world of various electronic communications, it is hard to beat the effectiveness of a personal visit.
Paul and Barnabas agreed that there was a need to go back and visit the brethren in the various cities they had preached, but they disagreed over whether or not John Mark should accompany them as he did on the first journey. John Mark had bailed out on them quite early during the first journey for some reason that Luke does not share (cf. Acts 13:13). However, whatever the reason was it is clear that Paul did not approve. Paul has no desire to take John Mark along again since he had already failed them once. Barnabas, on the other hand, sticks up for John Mark and, as a great encourager, is willing to give him another chance. Both Paul and Barnabas have made up their minds on this issue. Paul is as determined not to take John Mark with them as Barnabas is determined that he accompany them. The men are not able to come to an agreement since neither is willing to compromise on the matter. Their disagreement is very significant on this issue, so they decide to go their separate ways. Paul took Silas with him and headed north from Antioch. Barnabas took John Mark (who was his cousin) with him and headed southwest from Antioch. Both groups were determined to strengthen the churches as they traveled and make new disciples for the Lord. Paul and Silas went on their way with the blessings of the church at Antioch. The fact that there is no mention of such a blessing for Barnabas and John Mark may be telling. It may indicate that the brethren at Antioch viewed the matter as Paul did. However, it could simply be that the author is now fixing his attention upon Paul's history rather than that of Barnabas since this is where the two separate. Barnabas is not mentioned again in this book and we have no details of his further activities. It is impossible to conclude that either man was wrong here, particularly since Barnabas' decision may have proved best for John Mark in the long term.
There are some important lessons we can glean from this dispute: