Philemon is a book of the New Testament, the eighteenth in order, and the thirteenth of the letters attributed to the Apostle Paul. It's one of the shortest letters in the New Testament, at just twenty-five verses - a single chapter.
At its most basic level, Philemon is concerned with the discipline of a runaway slave - not the sort of thing you'd expect to occupy pride of place in the Christian Bible. However, as with all books of the Bible, progressive study uncovers further connections and meanings for the diligent student.
Philemon should be considered alongside Acts for historical context, and the letters to the Colossians and the Ephesians, which were written by Paul at the same time as the letter to Philemon (who was indeed a prominent member of the Colossian church).
Note: I've italicised the word 'Philemon' when referring to the letter, to distinguish from instances in which I'm referring to the man.
Background
Philemon is a letter from Paul and Timothy to Philemon, Apphia, Archippus and the Colossian church (Colosse was a city in the south-west of Asia Minor, present-day Turkey); however, the bulk of the letter is addressed directly from Paul to Philemon. Philemon's name means "friendly", and Paul addressed Philemon as a dear and beloved friend. This letter was delivered to the Colossians by Tychicus and Onesimus.
Philemon was written during Paul's first imprisonment in Rome, about A.D. 60, when he had been a Christian for nearly 30 years. Additionally, Paul wrote Ephesians at this time, and with Timothy, he also wrote Colossians. At other times, the pair co-wrote 2 Corinthians and Philippians, and with Silas, 1 Thessalonians and 2 Thessalonians. Soon after Paul wrote Philemon, he was released from his house arrest.
Structure
Verses 1-2, from Paul and Timothy to the Colossian church: Greetings.
Verse 3, from Paul and Timothy to the Colossian church: Blessing.
Verses 4-7, from Paul to Philemon: Christian union.
Verses 8-9, from Paul to Philemon: Christian duty.
Verses 10-14, from Paul to Philemon: Free will.
Verses 15-16, from Paul to Philemon: Salvation.
Verses 17-21, from Paul to Philemon: Christian influence.
Verse 22, from Paul to the Colossian church: Administrivia.
Verses 23-24, from Paul to the Colossian church: Greetings.
Verse 25, from Paul and Timothy to the Colossian church: Blessing.
Onesimus
A Christian, Philemon was a wealthy Greek landowner, in whose house the Colossian church met. Apphia and Archippus were probably Philemon's wife and son, respectively.
Onesimus had been one of Philemon's slaves who had stolen from him, and then run away, eventually to Rome. In Rome, he met Paul, who was subsequently instrumental in Onesimus' belief in Christ.
Paul believed that Onesimus should honour his legal commitment to Philemon by returning to his service. Since the law stated that a master had the right to execute a captured runaway slave, however, Paul decided to intercede on Onesimus' behalf.
Onesimus' name means "useful" and "profitable", and Paul played on these words to illustrate how Onesimus was now useful not just to Philemon, but also to Paul, and that Onesimus' sins had thus been turned to good by God. Paul asked Philemon to respect this turn of events when deciding how to deal with his returned slave.
Paul inferred that each individual Christian is free to act as he sees fit, according to a standard of morals that is known to all. Furthermore, he inferred that these acts of free will should not be overruled by other Christians, but that each Christian should conscientiously endeavour to do the right thing according to his or her own understanding.
Perhaps with Onesimus' case in mind, Paul wrote to the Colossians at this time that "In this new life, it doesn't matter if you are a Jew or a Gentile, circumcised or uncircumcised, barbaric, uncivilized, slave, or free. Christ is all that matters, and he lives in all of us."
In his letter to Philemon, Paul referred to the union that Christians have in Christ, a common spirit that binds them together, deepens their understanding of their Christianity and allows them to positively affect each other's lives.
Paul also wrote to the Colossians about the practical matters concerning masters and slaves: "You slaves must obey your earthly masters in everything you do. Try to please them all the time, not just when they are watching you. Obey them willingly because of your reverent fear of the Lord. Work hard and cheerfully at whatever you do, as though you were working for the Lord rather than for people. Remember that the Lord will give you an inheritance as your reward, and the Master you are serving is Christ. But if you do what is wrong, you will be paid back for the wrong you have done. For God has no favorites who can get away with evil. You slave owners must be just and fair to your slaves. Remember that you also have a Master - in heaven." Paul wrote similar advice in his letter to the Ephesians.
Greetings
At the close of the letter, Paul also passes on greetings to the Colossian church from Epaphras, Mark, Aristarchus, Demas and Luke.
Epaphras, who was with Paul in prison, had been the founder of the Colossian church; it was his report to Paul about the Colossians' struggles that precipitated Paul's letter to the Colossians. (Paul evidently never visited Colosse.)
Mark, Barnabas' cousin, had accompanied Paul and Barnabas on the first stage of their first missionary journey, but had deserted them before they got very far. When setting out on their second journey, Barnabas again wanted Mark to accompany them, but Paul would not allow it, and Barnabas therefore departed from Paul and took Mark with him on his own missionary journey. (At that time, Paul was joined for the first time by Silas.) By the time of Paul's first imprisonment in Rome, however, Mark was back in Paul's service, and he made himself available as his faithful assistant throughout the rest of Paul's life. Mark was also a sometime assistant of Peter, who eventually inspired him to write the Gospel of Mark.
Aristarchus was a Thessalonian who joined Paul sometime before or during Paul's third missionary journey. He was present on the occasion of the infamous craftsmen's riot in Ephesus, and continued to travel with Paul throughout Macedonia and Greece, back to Asia Minor, then to Jerusalem and finally to Rome, where he was voluntarily imprisoned with Paul.
Demas was an assistant of Paul who later deserted both Paul and Christianity.
Luke, a doctor, was a longtime travelling companion of Paul whose presence is felt at various stages throughout the Acts of the Apostles, which he authored (he was also the author of the Gospel of Luke).