Jim discusses the descriptions of Demas and Mark in the closings of a couple of Paul's epistles. Demas forsook Paul because he loved this present world. Mark, abandoned Paul at one point, but returned to be a faithful servant.
23 There salute thee Epaphras, my fellowprisoner in Christ Jesus; 24 Marcus, Aristarchus, Demas, Lucas, my fellowlabourers.
9 Do thy diligence to come shortly unto me: 10 For Demas hath forsaken me, having loved this present world, and is departed unto Thessalonica; Crescens to Galatia, Titus unto Dalmatia. 11 Only Luke is with me. Take Mark, and bring him with thee: for he is profitable to me for the ministry.
10 Aristarchus my fellowprisoner saluteth you, and Marcus, sister’s son to Barnabas, (touching whom ye received commandments: if he come unto you, receive him;) 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. 12 Epaphras, who is one of you, a servant of Christ, saluteth you, always labouring fervently for you in prayers, that ye may stand perfect and complete in all the will of God. 13 For I bear him record, that he hath a great zeal for you, and them that are in Laodicea, and them in Hierapolis. 14 Luke, the beloved physician, and Demas, greet you.