Oecumenius : John, called Mark, was accompanying them on the evangelic journey, from Palestine as far as Pamphylia. Then, finding the apostles' route too strenuous, and his spirit unbending toward those engaged in struggles, Mark, being a man given to exhaustion and not suited to so laborious a road and to the challenges and dangers that arise in each city, withdrawing from the apostles' route, returned to Palestine, not denying Christ, but renouncing the long and heavy road. Paul and Barnabas, full of the fruits of devotion, and preaching to the church in Jerusalem, in no way resolved to forbid hardships. When, then, all the nations were praising Paul and Barnabas for their accomplishments, Mark, being distressed, suffered a blow to his spirit, and perhaps thought within himself, saying, If I were a sharer in the sufferings, I would now be a sharer also in the praises; and he determined to accompany the apostles in their preaching. Barnabas therefore received him after his repentance, but Paul insisted and said, One who did not accompany us in the Lord's work should not be taken along. The contention, then, was one of righteousness, not of passion. For Paul sought what was just, and Barnabas what was compassionate. Mark accordingly followed Barnabas, striving and running, while Paul in the churches commanded that Mark be not accepted, not so that he might grieve him, but that he might make him more earnest. But when Paul saw that Mark had anticipated the urgency and had made his defense through others, he began to praise him and said, "Mark, Barnabas's nephew, sends his greetings; concerning whom you received instructions, if he comes, welcome him." (Col. 4:10) [CHRYSOSTOM] — Commentary on Acts