But I preferred to do nothing without your consent, in order that your good deed might be voluntary and not something force. Perhaps this is the reason he was separated from you for a while, so that you might have him back forever, no longer as a slave but as more than a slave, a beloved brother-especially to me how more to you, both in the flesh and in the Lord .
Now we can possibly get to the reason why Paul is negotiating for Onesimus. The text makes it clear that Onesimus was a slave to Philemon and we can infer that Onesimus had escaped from his master. According to Roman law, it was a criminal offense punishable by the death penalty for a slave to escape from his master. The escape by Onesimus had deprived Philemon of a worker and an asset. This is was a serious offense and no wonder why Paul is seriously negotiating on behalf of Onesimus. It was also illegal for Paul to give refuge to a runaway slave. Therefore, as Paul negotiates for Onesimus, he also follows legal procedures to help Onesimus to gain forgiveness and legitimate freedom.
By using the phrase ´departed for a while´ Paul is softening the gravity of Onesimus´ offense. Is Paul maintaining the status quo of supporting the evil system of slavery by sending Onesimus back to his master? Paul strategically negotiated for the freedom of Onesimus from the system of slavery. Philemon is now being asked to receive Onesimus not as a slave but as a brother. There is now a change of relationships here; Philemon the master who lost a slave and Philemon the Christian who lost a brother. But doing this Paul is advocating for the abolishing of slave-master relationship. Two takeaways; 1. Advocating for change of systems can happen easily within the confines of the laid legal structures. 2. Changing evil systems is a process that needs patience and wisdom