Colossians 4:11
And Jesus, which is called Justus, who are of the circumcision. These only are my fellowworkers unto the kingdom of God, which have been a comfort unto me. And Jesus, which is called Justus, who are of the circumcision. These only are my fellowworkers unto the kingdom of God, which have been a comfort unto me.
The verse names Jesus called Justus, a fellow Jew, as one of Paul's fellow workers unto the kingdom of God who had been a comfort to him. He belonged to the small group of assistants who stood by and supported Paul at Rome. The verse also counts Mark among those fellow workers who comforted and upheld Paul during his imprisonment, with Luke, Timothy, Tychicus and Demas, aiding him personally and sustaining his labor for the churches.
Mark is identified with Jesus Justus. He had earlier separated from Paul, unwilling to press on and deserting the missionary journey. Paul afterward welcomed and received him back, and the two were reconciled.
That earlier failure did not bar Mark from becoming a useful, trusted and valuable minister and gospel worker. Near the close of his life Paul called him profitable and useful for the ministry.