While in prison, Paul wrote a letter to Philemon to address a situation about a runaway slave named Onesimus.

Therefore, although in Christ I could be bold and order you to do what you ought to do, yet I prefer to appeal to you on the basis of love. It is as none other than Paul—an old man and now also a prisoner of Christ Jesus— that I appeal to you for my son Onesimus, who became my son while I was in chains.  Formerly he was useless to you, but now he has become useful both to you and to me.  Philemon 10-11

            It appears Onesimus ran away and got saved by Paul.  His name meant “useful” but as a runaway he became “useless.”  Slaves were property to the master because they were working off a debt.  The law said you could kill a runaway slave.  But Paul felt Philemon would do the right thing if Onesimus returned to Philemon, a sinner seeking grace.  Philemon knew about grace since he too was a follower of Christ.

I am sending him—who is my very heart—back to you. I would have liked to keep him with me so that he could take your place in helping me while I am in chains for the gospel.  But I did not want to do anything without your consent, so that any favor you do would not seem forced but would be voluntary.  Perhaps the reason he was separated from you for a little while was that you might have him back forever—no longer as a slave, but better than a slave, as a dear brother. He is very dear to me but even dearer to you, both as a fellow man and as a brother in the Lord. Philemon 12-16

            This is completely Philemon’s call—punishment or grace.  We believe Philemon chose grace because Paul mentioned Onesimus in another book, Colossians as a fellow worker.

            We can punish according the law—that's justice.  Or we can forgive according to God’s law—that’s mercy.