John Calvin on Colossians 4:14

14. Luke saluteth you. I do not agree with those who understand this to be Luke the Evangelist; for I am of opinion that he was too well known to stand in need of such a designation, and he would have been signalized by a more magnificent eulogium. He would, undoubtedly, have called him his fellow-helper, or at least his companion and participant in his conflicts. I rather conjecture that he was absent at that time, and that it is another of the same name that is called a physician, to distinguish him from the other. Demas, of whom he makes mention, is undoubtedly the person of whom he complains — that he afterwards deserted him. (2 Timothy 4:10.)