A re-uniting with Philemon would be the best option for Onesimus. Otherwise he would be living as a runaway for a long time, probably the rest of his life. Maybe he would have found another job sooner or later. But living with himself would be the difficulty. It often is.
It seems from these verses that Paul has persuaded himself that Philemon will comply with his request and accept Onesimus back into his service. But what if he did not? What if he refused? What if Onesimus was rejected? Without a job, or prospects? Condemned forever as a runaway slave?
It has often been suggested that the reason for Paul dictating his letters was an eye problem making it difficult for him to see. But his blindness was healed when Ananias laid hands on him. I think it is more likely that Paul dictated letters because his arms were chained.
One translation of partner gives comrade in arms. That speaks to me of soldiers in an army. In this case The Army of The Lord. The Greek word used for partner in this verse is koinonia. It is often used in the Christian community about working together and sharing everything.
We get the impression that Onesimus had served Paul during a reasonable period of time. The life change that Jesus had obviously brought about in this former slave is a message to all who read this short epistle. That giving your life to Jesus can bring about huge changes.
This verse makes me think of my childhood and youth. I remember people giving me a choice which went like this:- You can have whichever you like, but take this one! Or something similar. Paul asks Philemon for a favour, and says it is your choice, but please do this!!
At the beginning of these verses we see a description of this new convert; his very heart. Onesimus must have used his experience as a slave to serve Paul in any way he could. Paul was blessed and impressed and was trying to persuade Philemon to accept the new Onesimus.
Up to now Philemon has been personal compliments and encouragements. Here we read the reason Paul is writing to Philemon. In the original Greek, it reads as a play on words. The name Onesimus means useful or profitable. Paul is obviously hoping that his words will make the reader smile.
Paul was imprisoned in Rome under Roman authorities. But he did not consider that to be the reality of his situation. Paul was confident that Jesus was with him in any and every situation, and he made the most of them all. That is a challenge for many believers today.
This letter gives us a glimpse of the changes which are still ongoing in Paul. We see the old Paul, known for his aggression and religiosity, certainly not for his love! The new Paul is encouraging Philemon to take Onesimus back into his employ. We are all on the road.