Culled from Albert Barnes NT Commentary
Aristarchus was of Thessalonica, and is mentioned in Ac 19:29; 20:4, as Paul's companion in his travels. In Ac 27:2, it is said that he accompanied him in his voyage to Rome, and from the passage before us it appears that he was there imprisoned with him. As he held the same sentiments as Paul, and was united with him in his travels and labours, it was natural that he should be treated in the same manner. He, together with Gaius, had been seized in the tumult at Ephesus, and treated with violence; but he adhered to the apostle in all his troubles, and attended him in all his perils. Nothing further is certainly known of him, though the Greeks say that he was bishop of Assamea in Syria, and was beheaded with Paul at Rome, under Nero." Calmet.
John Mark, in relation to whom Paul and Barnabas had formerly disagreed so much as to cause a separation between Barnabas and Paul. The ground of the disagreement was, that Barnabas wished to take him, probably on account of relationship, with them in their travels; Paul was unwilling to take him, because he had, on one occasion, departed from them. They afterward became reconciled, and Paul mentions Mark here with affection. He sent for him when he sent Tychicus to Ephesus, and it seems that he had come to him in obedience to his request. Mark had probably become more decided, and Paul did not harbour unkind and unforgiving feelings towards any one.
If he come unto you, receive him. Paul here intimates that he was about to leave Rome, and he enjoins it on the Colossians to receive him kindly. This injunction may have been necessary, as the Colossians may have been aware of the breach between him and Paul, and may have been disposed to regard him with suspicion. Paul retained no malice, and now commended in the warmest manner, one from whom he was formerly constrained to separate.