In New Testament times, households often included slaves, and many of these slaves became Christians. One slave who became a Christian was Onesimus.
Onesimus had worked in Colossae for a man named Philemon, but he ran away and came to Rome. There he met Paul and was converted. Paul knew Philemon, so when Onesimus decided to return to his master, Paul wrote a letter to Philemon, urging him to forgive Onesimus and receive him back (Philem 10-19; for details see PHILEMON).