It was only a matter of time before Barnabas and Paul would have split with each heading up his own evangelistic effort, thus training other brethren to labor in the glorious work of Christ, and bringing his Name to places where he was not known. Nevertheless, Luke makes a point of showing that this separation took place earlier than it would have under natural circumstances, and he uses Mark as the impetus in that division.
The division is put into the context of the threat of dividing the Jewish and gentile believers. We can only speculate about why Paul was so adamant about not taking Mark, but I believe, through his placement of the surrounding events, Luke implies Mark played a major role in bringing to pass those events which brought about the need for the Jerusalem Council. Moreover, how Mark is introduced in Acts 12 seems to give him an important status when we should not even know him, if Luke’s work follows an exact chronological order, but it doesn’t. Acts 12 is a pivotal chapter where Luke changes from recording the ministry of Peter to recording that of Paul, and, as was done in literary works of that day, some overlap was used to bring the two accounts together. How should we understand this? It would be foolish to place our speculations in cement, saying **this** is what occurred, but, if what Luke leads us to believe is actually true, he tells us that what we do and what we say concerning one another can have significant consequences, and we need to beware.
Acts 15:37 puts Mark in Antioch, where he had been in Acts 13 at the beginning of Luke’s first recording of Paul’s missionary efforts (cp. Acts 13:5). There he is called John and is so called in verse-13 as well. However, this same John is introduced to us in Acts 12:12, where Luke says he was surnamed (G1941) Mark. Markus is a Roman name, so John would not be called Mark in Jerusalem, because that name would imply he approved of Roman occupancy of the Holy Land. The Greek word used for surnamed is also used in Acts 4:36 for the Apostles calling Joseph by the name Barnabas. So, it seems that Luke is telling us in Acts 12:12 that John already has the surname Mark, but if he wasn’t given this name in Jerusalem, he had to have been given this name later. But, when would his have been?
If Luke is showing us that John, surnamed Mark, is embarking on an evangelistic ministry for the first time in Acts 13:5 and was at this time known as John, then his name Mark was given him later, sometime after the Galatian ministry. While we may postulate many reasons why the Latin name Mark would have been given him, ranging from the mark given Cain in Genesis 4 to the mark given Job by God to endure suffering for a divine purpose, the fact remains that we do not know why he was given this surname. Nevertheless, it seems logical that the name Mark, since it is a Roman name that would not have been used in Jerusalem where he had lived, was given John sometime after his departure from Paul and Barnabas at Perga in Pamphylia (Acts 13:13).
A reasonable claim, then, can be made that Acts 12:25 also refers to a time after that first missionary journey and to Paul’s second visit to Jerusalem for both the famine-relief effort and for the Jerusalem Council. I think it is significant that Luke refers to Mark by only by his Hebrew name, John, in Acts 13:5 and Acts 13:13, but in Acts 12:12 and Acts 12:25 he not only calls him John but also states he has the surname, Mark. Luke does this for a third time in Acts 15:37, but from Acts 15:39 and onward John is not called by his Hebrew name again, but is thereafter known as Marcus or Mark (cp. Colossians 4:10; 2Timothy 4:11; Philemon 1:24; 1Peter 5:13).
If these comparisons point to a logical conclusion, then John (Mark) was keenly observed for awhile by Paul and, by implication, gentile believers who knew his history, to ascertain that he was a true brother in Christ. Barnabas, that son of consolation, knew Mark’s heart from the beginning, but Paul had his doubts. Neither, however, would deviate from the stand he had taken and so they separated. Nevertheless, this separation was not so unfriendly that it should mean they separated one from another, never again to speak to the other. No, this should be seen in the manner in which we view the separation of the Hellenist believers from the Hebrew believers in Acts 6. It is a friendly one, and Paul refers to Barnabas in 1Corinthians 9:6, as someone the Corinthians should have known, because he labored among them, just as Paul had done, i.e. without their financial support. So, Paul’s reference could be seen as he and Barnabas working together from time to time after this incident involving John Mark. Moreover, Paul also came to view Mark as a trusted fellow laborer, as the above Scriptures imply.
 “For, though all parts must be independently perfected, when the first is complete the second will be brought into essential connection with it, and attached like one link of a chain to another; there must be no possibility of separating them; no mere bundle of parallel threads; the first is not simply to be next to the second, but part of it, their extremities intermingling.” [The Way to Write History 55; Lucian of Samosata; cir. 120 CE to 180 CE (emphasis mine)]. The complete work can be found HERE. The point is Luke was following a rule of ancient history by overlapping the accounts of Peter and Paul; so the events of Acts 12 are intermingled with the account of Paul’s ministry to Galatia in Acts 13 through 15 with Barnabas taking Mark with him back to Antioch (Acts 12:25) after the Jerusalem Council with the next chronological event being Acts 15:30.