This letter shows Paul's passion for looking after those who were powerless. He does an amazing job of defending Onesimus while addressing Philemon in a respectful and encouraging way. We could learn from this when we are fighting someone else's corner.
Philemon was a well-known Christian and probably a member of the church at Collossae. He also owned a slave called Onesimus. Onesimus had run away from his master, met Paul and become a believer in Jesus. Paul wrote to Philemon, asking him to welcome Onesimus back as a member of the Christian family.