Philemon was a lay leader in the church at Colossae. This letter concerns a slave he owned named Onesimus (v. 10). Onesimus had run away but, coming into the company of Paul, had become converted.
Paul is now sending Onesimus back, along with this letter. It is a personal appeal to Philemon, to treat his slave as a Christian brother. The social influence of the Gospel is evident, in both the example of Paul and his entreaty.
Unlike many NT epistles, few modern scholars doubt the authenticity of Philemon: “No serious objection stands in the way of receiving this letter as genuine” (Martin, 153).
Philemon has close connections with Colossians. Both letters include greetings from Epaphras, Mark, Aristarchus, Demas, and Luke (see vv. 23-24). Archippus, who is given a special word of instruction in Col 4:17, is one of the persons addressed in Philemon (v. 2). Onesimus likewise is named in both letters, as being sent back by Paul to Colossae (vv. 11-12; cf. Col 4:9). Most probably, Philemon was written and sent at the same time as Colossians—while Paul was a prisoner in Rome, ca. a.d. 62.