When Paul wrote his short note to his friend, Philemon, I cannot imagine that he expected it to end up canonized (if he expected any of this writings to be canonized) and cherished by Christians for the past many centuries. Most of the time it has been forgotten because as compared to the larger Pauline corpus, it simply lacks of theology. In practical theology, however, those actions by the Christians community regarding everyday life, it abounds in treasures rediscovered every so often.
The occasion of the letter is simple: A slave had escaped Philemon’s care, making his way to Paul, had been converted to Christ. Now, it was time to answer to legal authorities and return to Philemon to receive whatever punishment he was due. Conversion, or repentance, clears the account with God, but in no way should be thought of allowing someone to ignore their obligations to the earthly authorities. Paul’s letter was a soft, yet stern, admonition that while the social orders of the world did not change, the fact that Onesimus had changed – he had become a follower of the Way, and now, the hope was that Philemon would receive not as the former slave, but as the new brother – did not negate his duty to the secular world.
v16. Not as a slave any longer, but someone more than a slave — a brother beloved, especially to me, but so much more to you, both in the flesh and in the Lord! (Translation mine)
Further, he goes on to ask that Philemon receive the new Christian as he would the aged Apostle. For Paul, there was indeed no slave or free in Christ although he recognized that they existed in the secular world.
What Paul did, and enforced, was the idea that Christians can seek forgiveness and be granted it from God, but also surrendered to the authority of secular authorities for any crimes committed. Onesimus was a slave, and had escaped. This was his crime. Yet, he had met Paul, converted, and still had to face whatever punishment Philemon would have given out. It was not for Paul to declare Onesimus innocent of the crime simply because he had become a Christian, but it was Paul’s duty to, as he set in the chains of the secular world, make sure Onesimus faced up to his pre-existing obligations.
Further, we note that it was not merely the escape to (true) freedom, but also a theft which Onesimus had to recompense.
v18. If he has wronged you, or if he owes you something, put it on my account
I know of a pastor who, while failing to understand the seriousness of child molestation, believes, and have fought for, the idea that since the child molester has repented, then he should be spared any civil or criminal processes. This is directly contrary to what Paul forced Onesimus to do. Paul obeyed the laws of the land – if they were not against God – and demanded that the Church did as well. Paul could easily have kept Onesimus with him, defying the laws of Rome, but he did not. Paul was obligated to keep the laws of the land, as a Christian and then as a Roman citizen. Do you think he would have allowed that repentance mitigated any obligations to the secular world? By example, we know that he would not.
Tradition states that Onesimus returned to Philemon and was freed. He later became Bishop of Ephesus, after Timothy, and found the martyr’s end. None of this would have been possible had Onesimus not met his Christian obligation to the Secular World.