The short letter to Philemon is the most personal of all of Paul’s preserved writings. In his three decades of ministry, Paul certainly wrote many other short notes and personal letters, but God chose to keep only this one for our benefit. Although nowhere does this letter give the location of Philemon, Colossians 4:7-18 provides a list of names almost identical to those in Philemon, including Philemon’s slave, Onesimus. It seems that Paul sent Tychicus and Onesimus back to Colossae with two letters – one for the whole church (Colossians) and one for Philemon.
The purpose of this letter was three-fold. First, because Onesimus had run away from Philemon (presumably having stolen some money), Paul needed to return him to his rightful owner (vs. 12, 14). Regardless of our beliefs about slavery, this was the right thing for him to do, given the culture in which they lived. (The comment in Colossians 4:1 about how masters should treat slaves is not coincidental.)
Second, Paul wanted to personally vouch for Onesimus’ conversion to Christianity. He had been saved through Paul’s ministry, while Paul was under house arrest in Rome (vs. 10, 15-16; Acts 28:16, 30-31), and Paul insisted that he be the one to tell Philemon. (Philemon almost certainly would not have believed Onesimus, thinking it was an act to secure his pity.)
Third, Paul wanted to ask for Philemon to pardon Onesimus for his crimes (at least theft and running away). Although Philemon owed Paul a great spiritual debt, Paul promised that he would personally repay Onesimus’ financial debt, should Philemon choose to pursue it (vs. 18-19).
It is often charged that Paul should have done something more to secure Onesimus’ freedom. Opponents of Christianity point to Paul’s silence and condemn the Scriptures for condoning slavery. In reality, Paul acted exactly as he should have in this matter. Slavery is not a sin and was often mutually beneficial to both the master and the slave, depending on the circumstances. The sin was in how cruel masters would treat their slaves, something that Paul clearly addressed both here and in Colossians 4:1, as well as in other letters. However, verse 21, which is often overlooked, contains an implication that Philemon should treat Onesimus far better than he was required by Roman law. Although we cannot say that Paul necessarily meant that Philemon should completely pardon and free Onesimus, the suggestion is certainly there, and Paul allowed the Holy Spirit to place that conviction on Philemon, if that was what God wanted.
Thus, this brief letter demonstrates that even our social and economic decisions are to be ruled by biblical truth. It also provides an example of how believers can tactfully and lovingly point out truth and error to help our fellow believers live godly in this world.