It is now generally regarded as one of the undisputed works of Paul. It is the shortest of Paul's extant letters, consisting of only 335 words in the original Greek text, and twenty-five verses in modern English translations.
Paul, who is apparently in prison (probably in either Rome or Ephesus), writes to a fellow Christian named Philemon and two of his associates: a woman named Apphia, sometimes assumed to be his wife, and a minister named Archippus (see Colossians 4:17). If the letter to the Colossians is authentically Pauline, then Philemon must live in Colossae. As a slave-owner he would have been wealthy by the standards of the early church and this explains why his house was large enough to accommodate church meetings (v. 2). Paul writes on behalf of Onesimus, Philemon's slave. Beyond that, it is not self-evident as to what has transpired. Onesimus is described as having been "separated" from Philemon, once having been "useless" to him (a pun on Onesimus's name, which means "useful"), and having done him wrong.
The dominant scholarly consensus is that Onesimus is a runaway slave who became a Christian believer. Paul now sends him back to face his aggrieved master, and strives in his letter to effect reconciliation between these two Christians. What is more contentious is how Onesimus came to be with Paul. Various suggestions have been given: Onesimus being imprisoned with Paul; Onesimus being brought to Paul by others; Onesimus coming to Paul by chance (or in the Christian view, by divine providence); or Onesimus deliberately seeking Paul out, as a friend of his master's, in order to be reconciled.
There is no extant information about Onesimus apart from the letter. Did he return to Philemon? Were they reconciled? Did Onesimus begin missionary work alongside of Paul? These remain at present open questions. Ignatius of Antioch mentions an Onesimus as Bishop of Ephesus in the early second century. It was suggested by some Bible scholars in the 1950s that these this Onesimus is the same as the Onesimus in Paul's letter. Furthermore, it was suggested that Onesimus could have been the first to compile the letters of Paul, including the letter that gave him his own freedom as an expression of gratitude. This hypothesis could explain why the letter to Philemon (a letter written to an individual) is included alongside letters written to Christian communities.
Paul's letter is a personal one and can appear cryptic to outsiders. His tactful address to Philemon was labelled "holy flattery" by Martin Luther. Commending Philemon's Christian compassion, but at the same time subtly reminding Philemon of his apostolic authority over him, and the spiritual debt Philemon owes to him, Paul pleads with Philemon to take Onesimus back. Paul notes that because of his conversion, Onesimus is returned "no longer as a slave but more than a slave, a beloved brother" (v. 16). Several issues remain unclear about Paul's expectations for Philemon. Is he expected to forgive Onesimus or Manumit him? Is he to consider Onesimus to be Philemon's "brother" as well as his "slave"? Does this new brotherhood supplants his servitude? Some fascets of Paul's societal expectations can be seen in these verses.
The German Protestant theologian Martin Luther saw a parallel between Paul and Christ in their work of reconciliation. However, Luther insisted that the letter upheld the social status quo: Paul did nothing to change Onesimus's legal position as a slave—and he complied with the law in returning him.
The letter was a cause of debate during the British and later American struggles over the abolition of slavery. Both sides cited Philemon for support.