Good works can't be forced. They can't be an obligation or come from pressure. For it to count as righteousness, it must be an act of personal conscious choice. This is why Paul relinquishes Onesimus to Philemon. He does so explaining that this once worthless slave, is no so valued (through salvation) that Paul would have like to keep him on to help with the work of the gospel.
So far, Paul has entreated to his relationship with Philemon, appealed to his sense of responsibility as a believer, and pointed out the change in relationship that now exists between master and slave. He then goes on to address the more pragmatic aspects of the rift.
So if you consider me a partner, welcome him as you would welcome me. If he has done you any wrong or owes you anything, charge it to me. I, Paul, am writing this with my own hand. I will pay it back—not to mention that you owe me your very self.What clever and direct way to lay out his expectations and cleanly deal with the practical side of this reconciliation.
This letter from Paul summarizes so precisely our relationship with our Savior, so cleanly our position in Salvation, so richly our value even as slaves. It takes faith to see so clearly, faith to walk so purely.
"For we are all His Onesimi, to my thinking."
-- Martin Luther