13:5 Who is this John?

This is still John Mark, Barnabas' cousin, who wrote the gospel of Mark. Paul and Barnabas took him back to Antioch with them after they finished taking the relief money to Jerusalem (CP 11:27-30).

Mark accompanied Paul and Barnabas on their first apostolic mission in 13:5, but left them soon after, in Perga (CP 12:25-13:5, 13).