The letter from Paul to Philemon was written around 59–61 AD while Paul was a prisoner in Rome. Philemon was the master of the slave Onesimus. Paul met Onesimus after he had run away from his master, and Onesimus had subsequently become a Christian. Now he is willing to return to his master, and Paul very tactfully asks Philemon to receive him as a brother. By Roman law he could have had the runaway slave put to death.
Paul, writing from prison, identifies himself as being the prisoner of the Anointed. He includes Timothy as co-author, and writes not only to Philemon but also to a woman named Apphia, to another co-worker named Archippus, and to all the believers. Though the content of the letter is primarily to and about Philemon, the others are to read it and learn from it.
Onesimus was one of Paul’s converts to Christianity. Paul could have pulled rank on Philemon but instead appeals to him out of love, to accept the former escaped slave back as a brother. Notice that Paul also uses a little leverage by mentioning his being old, as if to say, “Do this favor for an old man, will you?”
The name Onesimus means “useful”, and Paul uses a play on words in saying that although he was formerly useless, he was now living up to his name. Paul wanted to return him to his owner instead of just keeping him as a helper without first having Philemon’s consent.
Paul offers, in strict legal terms, to reimburse Philemon for any hardship he may have suffered due to the temporary loss of Onesimus’ services. But he adds yet more leverage: Philemon owed him his life! Paul is cashing in on any favor he could in order to motivate Philemon to do the honorable thing as a Christian. And on top of that he informs Philemon to prepare a room for his impending visit, so he can be there in person to see what Philemon chooses to do.
Paul gives the usual greetings, from himself and others with him.