What of Onesimus?

Today we come to the main reason for Paul's letter to Philemon.

8Accordingly, though I am bold enough in Christ to command you to do what is required, 9yet for love’s sake I prefer to appeal to you—I, Paul, an old man and now a prisoner also for Christ Jesus— 10I appeal to you for my child, Onesimus, whose father I became in my imprisonment. 11(Formerly he was useless to you, but now he is indeed useful to you and to me.) 12I am sending him back to you, sending my very heart. 13I would have been glad to keep him with me, in order that he might serve me on your behalf during my imprisonment for the gospel, 14but I preferred to do nothing without your consent in order that your goodness might not be by compulsion but of your own accord. 15For this perhaps is why he was parted from you for a while, that you might have him back forever, 16 no longer as a slave but more than a slave, as a beloved brother—especially to me, but how much more to you, both in the flesh and in the Lord.

17So if you consider me your partner, receive him as you would receive me. 18If he has wronged you at all, or owes you anything, charge that to my account. 19 I, Paul, write this with my own hand: I will repay it—to say nothing of your owing me even your own self. 20Yes, brother, I want some benefit from you in the Lord. Refresh my heart in Christ.

21 Confident of your obedience, I write to you, knowing that you will do even more than I say. 22At the same time, prepare a guest room for me, for I am hoping that through your prayers I will be graciously given to you.

There is a man named Onesimus.

This is a man known to Philemon, a man Philemon deemed as useless. This man has become a useful person to Paul and as such, Paul is wanting to send him back to Philemon, not as a slave, but as a useful person. He is asking Philemon's permission to do so, but as he asks he removes Philemon's possible reasons to say no.

• Onesimus is no longer useless
• Paul will repay anything Onesimus owes
• He can be greeted (and therefore treated) as if he were Paul himself
• He is a brother in Christ
• Paul thinks of him dearly, like a father would a son.

So what to do with Onesimus?

We don't know from the letter what Philemon's response was.
But we can catch gleanings of what it should be.
Onesimus was once not a believer. But now he is. He is much loved by Paul. He is a brother in Christ. He should be greeted as one. He is a useful person now, not just a useless slave who was discontented and then ran away. Onesimus is returning to Philemon as a useful, contented man, a brother in Christ.
My guess is the Philemon said okay. :)
This I'm also thinking is what our response should be to wayward ones.
To welcome them as brothers in Christ when they become believers.
To not hold their pasts against them, but to see them for who they are now.