What does Acts 15:38 mean?
Paul and Barnabas are planning a second missionary voyage. In the first, they sailed east to the island of Cyprus, then north to Pamphylia on the south-central coast of modern-day Asia Minor. From there, they moved north and planted several churches in the region of Galatia. After back-tracking to encourage the new churches, they sailed home to Syrian Antioch (Acts 13—14).When they set out, Barnabas' young cousin John Mark went with them. Mark was from Jerusalem; his mother, Mary, owned the house where Peter fled when the angel released him from prison (Acts 12:12). Some think Mary also hosted Jesus' Last Supper (Mark 14:14–15). Mark wrote the gospel bearing his name, likely recording the accounts of Peter. And some think he is the young man who ran away naked when Jesus was arrested (Mark 14:51–52).
But something happened when Paul, Barnabas, and Mark left Cyprus. When they reached the mainland, Mark abandoned them and returned home (Acts 13:4). His actions were so abrupt and unexplained that scholars speculate he was motivated by something more than simple homesickness.
Now, Barnabas wants to give him a second chance. Paul disagrees. Barnabas refuses to back down. When the disciples refused to meet with Paul in Jerusalem, it was Barnabas who risked his life to see if the persecutor of the church had truly found faith in Jesus (Acts 9:26–27). Naturally, Barnabas would want to do the same for his cousin.
The truth is, Paul doesn't need Barnabas anymore. Barnabas apparently gave Paul an air of legitimacy in the Jerusalem council—see the "Barnabas and Paul" of Acts 15:12 and 25. But Paul had already taken the lead in evangelizing outside Judea—note the "Paul and his companions" of Acts 13:13 and "Paul and Barnabas" of Acts 13:43, 46, 50; 15:2. Paul is also seen as the primary spokesperson during their trip (Acts 14:12). Paul doesn't need any more encouragement or mentoring, but John Mark does.
Paul does need a tough partner who can withstand physical and spiritual persecution. Another Roman citizen would be a plus. That's what he finds in Silas (Acts 16:37). Silas will be with Paul in the prison in Philippi (Acts 16:19–34) and he'll remain with Timothy in Berea when Paul has to leave (Acts 17:14; 18:5).
In the Christian life, God sometimes brings people into our lives for a defined period. Despite Paul and Barnabas' "sharp disagreement" (Acts 15:39), God planned for them to separate and go their own ways. Not every disagreement is a failure in our spiritual lives, Christians will not always be called to work in the exact same way as other believers. In such moments, we should sense the Holy Spirit calling two people in two different directions—if the paths are both spiritually valid, such things are not wrong.
The decision they make (Acts 15:39), in fact, seems to be the best possible response to the differing needs of Paul and Barnabas. Neither is condemning or interfering with the other. They simply resolve that it's time for each to pursue God's separate will for their ministries.