10I appeal to you for my child, Onesimus, whose father I became in my imprisonment.
The way in which Onesimus came into slavery is not clear. Most likely he was born into the system, though he could also be a prisoner of war or someone who voluntarily sold himself. Whatever the reason, he was a slave and he belonged to Philemon.
10 I appeal to you for my child, Onesimus, whose father I became in my imprisonment.