Philemon is the shortest of Paul’s letters, and is perhaps the most unusual.
Most of the letters written by Paul that made it into the New Testament were written to churches. You can tell by the way they are named: “Epistle to the Romans,” “Epistle to the Philippians,” “Epistle to the Colossians.” These letters were intended to be read aloud in front of congregations, and as such they feel a lot like sermons.
A few of Paul’s letters were written to younger ministers who were serving as church leaders - specifically Timothy and Titus. These letters are much more personal, as you would expect when a mentor is writing to his beloved students, but are still largely concerned with church affairs.
Philemon is the only letter of Paul’s that has survived that is written on a purely personal matter. Paul isn’t addressing the church, nor is he talking to one of the church leaders. Philemon - at least at this time - was merely a member of the congregation (though likely a wealthy one).
So, why does Paul write this letter? What is it about?
During his missionary journeys, Paul apparently encountered a man named Onesimus. This man was a fugitive slave: he had run away from his master but became a Christian when he heard Paul preach. Not knowing what else to do, Onesimus decides to travel with Paul - ultimately going all the way to Rome with him. While with Paul, Onesimus, which means “useful,” really lived up to his name, becoming not only a helper but a dear friend that Paul thought of almost as a son.
By coincidence or divine providence, the master that Onesimus ran away from was a Christian named Philemon that Paul not only knew, but whom Paul had led to Christ. When Paul decides to send a letter to Philemon’s home church of Colossae, decides to send Onesimus to deliver the letter. Paul also writes another letter - the one we know of as “Philemon” for Onesimus to take to his master.
Imagine for a moment what Onesimus must have felt as he walked up the steps of Philemon’s estate. As a runaway slave, Onesimus could be severely punished - even killed - for his actions. His only defense against his master’s wrath is a sealed letter that Onesimus hopes will protect him from his master’s wrath. What must have been going through his mind as he knocked on that familiar door? What does he say to the servant who answers it? What was in this letter that Onesimus was trusting to save his life?