Note: Since this letter is so short (only one "chapter"), references to Philemon normally indicate only the verse number(s), without a chapter number (e.g., not 1:3 but simply 3; not 1:6-8 but simply 6-8)
Letter Opening (1-7)
Sender & Recipient (1-2)
Formulaic Greeting (3)
Thanksgiving for Philemon's faith and love (4-7)
Letter Body (8-22)
Paul appeals to Philemon on behalf of Onesimus,
who is now a beloved brother in Christ (8-16)
Settling "accounts" between
Philemon and Paul, which will settle Onesimus' account as well (17-22)
Letter Closing (23-25)
Individual Greetings from Epaphras and four co-workers in Christ (23-24)
How one understands why the slave Onesimus was in jail with Paul greatly affects how one interprets the purpose of this letter.
Onesimus was a "runaway slave" who had fled from his master, Philemon.
Onesimus, a slave, had been sent on a mission by his master, Philemon.
He was caught and put into the same jail as Paul by coincidence.
Philemon had sent Onesimus to assist and care for Paul in jail.
Onesimus begged Paul to write to Philemon, to ask Philemon not to punish the runaway slave further after he is returned home.
Paul takes the initiative in writing to Philemon, to ask Philemon to set the slave free so he can become a Christian missionary.
He was also a thief who had stolen something from his master, Philemon.
He was not a thief, but probably a debt slave; thus Philemon would lose out if he set Onesimus free.
Onesimus' Later Life as a Christian:
Onesimus is mentioned one other time in the NT. At the end of Paul's letter to the Colossians, he mentions that he is sending Tychicus ("my beloved brother, trustworthy minister, and fellow slave in the Lord") together with Onesimus ("a trustworthy and beloved brother, who is one of you") as his messengers to the Christians in Colossae.
Later Christian tradition (after the NT) refers to Onesimus as the first "bishop" of the Christian Church in Colossae.
Having learned how slavery and prisons were very different in the Ancient World than we might have thought, read Paul's letter to Philemon again. Discuss which of the two interpretations listed above seems to make more sense.