Colossians 4:14

Luke, beloved physician, and Demas salute you. For a brief biographical sketch of Luke, see my Commentary on Luke, Introduction. Only in this place in the New Testament is Luke referred to as a doctor, or physician. Nevertheless, the undeniably medical cast of his vocabulary is a total corroboration of what is stated here.

And Demas salute you ... As Peake said:

Demas' being mentioned here without commendation is commonly explained as due to a foreboding of Paul that he would turn out badly, suggested by the reference in 2 Timothy 4:10.[23]

Harry Emerson Fosdick preached a sermon on the three New Testament references to Demas, calling them three points that enable the plotting of the parabola of Demas' life. The sermon is interesting enough but founded on a misconception. Philemon and Colossians were written at the same time and carried by the same messenger; and in the letter to Philemon, Demas is mentioned as a "fellow-laborer," and even before Luke! Still, it is tragic truth that Demas fell from whatever eminence he enjoyed in these passages, the reference in Timothy revealing that he forsook the apostle, "having loved this present age." There is an old tradition to the effect that he became the owner of a brothel in Dalmatia.