I appeal to you for my child, Onesimus, whose father I have become in my imprisonment.
Onesimus was a slave who ran away from his master, Philemon. Philemon was one of Paul’s disciples. So Onesimus, perhaps in a bid for sanctuary of some sort, ran to Paul. He lost a master and gained a father. His father eventually sent him back to his master, not as a slave, but as a brother. Tradition tells us Onesimus became the bishop of Colossae and was martyred for the Faith. Love is strong.