The answer is: His slave had run away

v10-12 - it is possible that the slave had stolen from his master (c.f. v18) and therefore run away as under Roman law this was punishable by death.

The New Testament letter to Philemon is a fascinating piece that really delves into the tense social issues of its time, particularly the phenomenon of slavery. Here’s where it gets really interesting: Paul, the letter’s author, not only addresses the immediate concern—onesimus, Philemon's runaway slave—but also subtly challenges the very foundations of social order.

While Paul is asking Philemon to forgive Onesimus and potentially even welcome him back as a brother in Christ, a significant fact to unpack is that the word “brother” in the Greco-Roman context was a revolutionary idea. For early Christians, this meant forming a new identity that transcended social hierarchies! Imagine Philemon’s social standing and expectations; he was a wealthy landowner, and suddenly, a power dynamic shift occurs if he’s supposed to regard Onesimus this way.

Another intriguing layer is the possible legal repercussions in Philemon’s context. Roman laws harshly punished runaway slaves, so when asking for mercy, Paul is indeed advocating for an act that went beyond law—it was an act of grace. Paul even offers to repay any debt Onesimus may owe underlining the principles of love, forgiveness, and faith in the early Christian community.

Emphasizing that everyone, regardless of status, should be treated with dignity continues to resonate through Christian history. It's one of those reminders that teachings of compassion and understanding were radical then and still pulse powerfully today!