On Paul and Barnabas’ first missionary journey, Mark had left prematurely, and now at the beginning of their second journey a dispute arises between Paul and Barnabas. Barnabas would like to bring Mark with them, but Paul disagrees. He feels that since Mark had previously abandoned them, that for this next journey Mark should stay home.
I have heard many a sermon where Barnabas is praised for his commitment to Mark, and Paul is blasted for his harshness. Mark later becomes successful in ministry, being the writer of the Gospel of Mark, and is later called on by Paul himself to come and minister with him. It is assumed that Barnabas was right and Paul was wrong. Barnabas’ name is translated as “the Son of Encouragement” and so it is further assumed that the key to training, mentoring, apprenticeship is encouragement. There are plenty of passages that confirm that encouragement is an important part of training.
The problem with this interpretation, besides it being speculative, is that the ministry of Mark from here on out is not defined by his relationship with Barnabas. It is only his relationship with Paul that is mentioned in 2 Timothy 4 and in Philemon 1.