Luke does not tell us why Paul and Barnabas decided to return to the church in Antioch that had sent them out on this missionary journey. Perhaps there had been an agreement as to how far they should travel or as to how long they would be away.
They returned to the places where they had established small churches. Maybe they had decided to give time to those groups in order to see if they had remained steadfast to their new faith. When they went to each location they discovered that the disciples there had remained true even although Paul and Barnabas had been forced to leave because of opposition. This is a reminder that God keeps his people.
Luke summarises the focus of the return journey under five spiritual activities. First, they strengthened the disciples, which would have included informing them of the great truths of the gospel. Second, they encouraged them to continue as disciples, and this would have included reminding them of the great reward that is waiting in heaven for faithful followers of Jesus. Third, they explained that troubles were more than unfortunate experiences – instead they were the God-chosen path for disciples to enter the kingdom of God, a reminder that such troubles test whether or not people are genuine in their commitment. Fourth, they organised the running of each congregation by appointing elders to look after each group. Fifth, they had a special time of prayer in each congregation – the fact that the prayer was accompanied by fasting indicates that the prayer time lasted more than a couple of hours! After that, they left the churches in the care of God, which is a reminder of their confidence in his commitment to his people.
Eventually they reached the sending church in Antioch and told them all that had taken place and that Gentiles were coming into the church elsewhere as they had in Antioch. Why did they give in their report? No doubt, they had a sense of accountability. No doubt, they were grateful for the many prayers that the church in Antioch had made on their behalf. And no doubt, they wanted the church in Antioch to use the information in their ongoing prayers for those other churches. This raises the question as to what we do with the information we receive about the Lord’s work elsewhere.