John Calvin Commentary Philemon 1:24

"[and so do] Mark, Aristarchus, Demas, Luke, my fellow-workers." — Philemon 1:24 (ASV)

Demas. This is the same person who afterwards forsook him, as he complains in the Second Epistle to Timothy (2 Timothy 4:10). And if one of Paul’s assistants, having become weary and discouraged, was afterwards drawn aside by the vanity of the world, let no one reckon too confidently on the zeal of a single year; but, considering how large a portion of the journey still remains to be accomplished, let him pray to God for steadfastness.