Aristarchus my fellowprisoner saluteth you, and Marcus, sister's son to Barnabas, (touching whom ye received commandments: if he come unto you, receive him;)
The Marcus spoken of here goes by a few different names. At times he is referred to as Marcus[Col 4:10, 1 Pet 5:13], other times John whose surname Is Mark [Act 12:12, Act 15:37], sometimes just John [Act 13:5, Act 13:13], and sometimes just Mark [Act 15:39, 2 Ti 4:11], but all of these titles are for the same man, the Gospel writer of the Book of Mark.
The first time he is mentioned is in Acts 12 when his mother, Mary, is hosting a prayer meeting in her house for Peter who is in prison. It is during this time that Paul and Barnabas meet Mark and return from Jerusalem with him. Our above verse sheds some light on the infamous events that took place in Acts 13 and the sharp contention between Barnabas and Paul in Acts 15. Barnabas did decide to take Marcus to Cyprus while Paul and Silas went on strengthening the brethren in the churches established on the 1st trip, but to accuse Barnabas of favoring family seems to be out of character. Barnabas was also the one who put his arm around Paul and introduced him to the Church and recommended him to the brothers. It is possible this relationship played some part in his decision-making but seeing that this young man grew up into a profitable minister and even author of Scripture is proof enough to me that Barnabas and Mark did not sail to Cyprus to vacation, rather Barnabas trained this man up into a profitable minister of the Gospel.
He is said to be a son to Peter, [1 Pe 5:13 The church that is at Babylon, elected together with you, saluteth you; and so doth Marcus my son.] In what sense we cannot be certain, other than he was considered as close as a son if not a biological son. Peter knew what it was to need a 2nd chance, perhaps when he saw Mark he was reminded of his desertion and how Christ gave him a 2nd chance at ministry. Some men are saved and go on serving God without any serious failings, others, like Peter, like Mark, and like myself have had seasons of serious failure but thank God for a Savior who comes to us and says “Lovest thou me?” “Feed my sheep,” and thank God for Barnabas's and Peter’s who don’t throw away young men who’ve made a mess of ministering.
Tradition holds that he gathered his information and inspiration for the Gospel that he wrote from his mentor Peter. Perhaps his gospel was Peter's retelling of the events. This would be in line with the “poor man’s language” used to write the Gospel and also with who the target audience seems to be, the common man, which Peter was. All of that is speculative but likely. We won’t be permitted to write any gospels but our life is a gospel lived out chapter by chapter, Be sure to make your mark on some Mark along the way.
There was a time that Paul would not have recommended Marcus, even as a helper, but notice what he says now, “(touching whom ye received commandments: if he come unto you, receive him;)" Apparently Mark had written to them, this could even be a reference to the Gospel he had written or letters written by him under the direction of Peter. The unfaithful, untrustworthy Marcus that Paul had known 30 years ago is a fully mature Gospel minister and Paul says “Receive him.”
It is no wonder this man became a profitable minister, He had a Godly mother, a preaching uncle, and Apostles for influence, we can see their fingerprints all his life. In Marcus, we can see the benefit of investing in people for the Gospel’s sake, even people who seem like they are not going to be profitable. A lifetime of Godly influence grew Marcus up into the “Fellow servant” and “Comforter” we see in the above text. This is the power of the gospel, not only to save sinners but to mature saints. Marcus’s life could be summed up with Philippians 1:6 “Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ:” Grace that saves, also secures and settles and the gospel work begins at salvation, but continues all our life long, forming us into “Fellow workers” and “Comforters.”