Paul writes his letter to Philemon asking him to receive Onesimus, to welcome him back. We don’t know exactly what has happened, but there has been some rupture between Philemon and Onesimus, leaving Philemon inclined to do the opposite.
We may safely assert a few other things about the situation Paul addresses, but I’d like to just toss this out there: What evidence within the letter supports the scenario whereby Philemon and Onesimus are master and slave? Is there any counter-evidence?
Further, is there any evidence to suggest that the two men are brothers? Again, what elements within the text rule out such a scenario?