Onesimus is a runaway slave—ran away from Philemon in fact. He has befriended Paul and become himself a Christian. Paul is writing to ask Philemon to forgive Onesimus, and take him back into his home, no longer as a slave or servant, but as a brother in Christ, an equal. Paul's words in his letter to the Galatians, where he claims that in Christ there is no slave,¹ are words he lives out here in his letter to Philemon. Interestingly, the sentiment on slavery expressed here and in Galatians is in stark contrast to the sentiment expressed in the pseudepigraphical first letter to Timothy where slaves are essentially told to know their place and do what they are told by their masters.² This is another example of how over just a few decades the church moved further away from the teaching of Jesus (and genuine Paul) and closer to the rules of Rome, ultimately being consumed by the empire.

The letter to Philemon though, asks its receiver to open his heart, to forgive past wrongs, to reconceive his relationship with this ex-slave in the light of equality in Christ. It's a big ask, indicating the bigness of heart we are expected to have if we wish to follow Jesus. Delusions of power, resentments and revenge have no place in the kingdom. Forgive us our trespasses as we forgive those who trespass against us.

¹ Galatians 3:28, There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
² 1 Timothy 6:1-4