4:2 Stay alert or “staying awake” refers to the mental attitude of expectancy and watchfulness.
4:3-4 An open door was a common expression for an opportunity for someone to do something (Ac 14:27; 1Co 16:9; 2Co 2:12). Paul asked believers to intercede for him so he could continue to spread the gospel. On mystery, see note at 1:26.
4:5-6 Paul’s final exhortation to the Colossians was that they would use wisdom in their interaction with unbelievers (1:9-10). The phrase making the most comes from a verb meaning “to buy up,” as if finding a bargain. Here it conveys the idea of making the most of one’s time spent with unbelievers.
4:7-8 Tychicus, a native of Asia, first joined Paul in Ac 20:4 and continued to serve alongside him (Eph 6:21; 2Tm 4:12; Ti 3:12). He may also have been the person who delivered this letter to the Colossians as well as the letter to the Laodiceans (see note at Col 4:16).
4:10-11 Aristarchus, a native of Thessalonica, was one of Paul’s companions and his fellow prisoner (Ac 19:29; 20:4). John Mark, the Gospel writer, joined Paul and Barnabas on their first missionary journey (Ac 12:12,25). Paul and Barnabas parted ways because Paul did not want Mark along for their second journey (Ac 15:37-39). These verses provide evidence that at some point Paul became convinced again of Mark’s usefulness. Jesus who is called Justus was a fellow Jewish believer.
4:15 Laodicea, ten miles from Colossae, also had a fledgling congregation of believers. Paul specifically mentioned Nympha, in whose home the Laodicean church met.
4:16 Once this letter had been read among the Colossian believers, they were to send it or a copy of it to Laodicea. Paul apparently wrote a letter to the Laodiceans that was also to be read in Colossae. The epistle to the Laodiceans was either another of Paul’s epistles (Ephesians?) or a letter that has not been preserved.
4:18 Although Paul probably used a secretary to write this epistle (cp. Rm 16:22), he often signed his letters himself as a mark of their authenticity and his affection for the recipients (1Co 16:21; Gl 6:11; 2Th 3:17; Phm 19).