It would all depend on the contents of the letter. By law, he knew he was as good as dead; the Roman empire had absolutely zero-tolerance for rebellious slaves. But he had returned anyway. With the letter. The letter he was watching Philemon read.
It was the right thing to do. Not that it had made the journey any easier. But he had to face his master and confess that he had sinned. He had run away. He had stolen. He was deserving of death.
Paul was responsible for this trip. And for the letter. Of course, he had been terrified when Paul had recognized him. The last thing a slave on the run wants to see is a familiar face. But he had been so kind. It was Paul that had introduced him to Jesus. But even as he had helped and served Paul, he knew there was a reckoning that awaited him. When Paul had suggested that he needed to return, he knew he must go.
Another slave had greeted him when he had arrived at the door. It was a familiar face, but he couldn't quite make out the expression. Was it fear? Was it contempt? Sympathy?
He looked at the letter in Philemon's hands. What did it say? He had traveled with it for so many days, but he had no idea what it contained. What could Paul possibly write that would deliver him?
Philemon placed the letter on the table and walked towards him. He stopped. Looked Onesimus in the eyes. Then he embraced him and kissed him on the cheek. “Welcome, brother,” he said.
The story of Philemon is a love triangle, of sorts. The book of Philemon deals with the complicated inter-relationships of three individuals. First, there is Philemon himself, a wealthy Christian living in Colossae and the recipient of Paul's letter. Philemon had a slave named Onesimus, the second vertex of the triangle, who has run away and probably stolen from his master. These acts of rebellion have put Onesimus under the penalty of death. Understandably, these are not conditions conducive to a healthy relationship.
Paul, by contrast, has an excellent relationship with both of these men. It would seem that Paul encountered Onesimus while he was on the lam and lead him to the Lord. Since that time, Onesimus has been helping Paul while he was imprisoned. We can speculate from his letter that Paul may have also lead Philemon to the Lord years earlier. Certainly, Paul writes of a strong and warm friendship with him.
Paul recognizes that these two alienated parties must be reconciled, so he sends Onesimus back to his former master armed with a letter. In it, Paul intercedes for Onesimus based on Philemon's love for Paul. He writes “Receive him as you would received me.” But Paul goes even further and offers to settle any outstanding debts, “If he was wronged you at all, or owes you anything, charge that to my account. I, Paul, write this with my own hand: I will repay it.”
The Epistle to Philemon reflects the greater story of the Bible, which also deals with three parties. We are Onesimus. We have wronged and run from God. Since the Bible teaches that our sin makes us deserving of death, we dare not return to Him on our own. Thankfully, we have a “mediator between God and men, the Man Christ Jesus” to restore the relationship we've broken. We can return in safety because Jesus tells the Father, “Put his sin on my account. Receive him as you would receive me.”