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 short, little letter to Philemon is a dramatic glimpse into the tension of first-century life. Picture this: Onesimus, Philemon’s runaway slave, takes a daring leap from servitude to search for freedom—much like running from a demanding job or relationship today. He might have encountered Paul—who was like a mentor, spreading messages of love and liberty—not through fancy letters or doctrines, but through sheer human connection.

Now, if Onesimus did take some property with him, it’s intriguing to learn that Roman law didn’t hold back on punishments. To look for freedom often came with monstrous risks; a possible death sentence hung over runaways. This showcases the harsh realities of those living in Roman times when they craved liberation from their untenable situations.

But there’s more! Paul advocates for Onesimus, asking Philemon to welcome him back—no longer just as a slave but as a beloved brother. This twist in the narrative illustrates the radical inclusivity of early Christian teachings. It suggests that personal relationships can supersede rigid societal structures.

In fact, the name “Onesimus” means “useful,” quite ironic given his status as a slave. Yet, in returning home, he becomes more than “useful.” Through this intertwined story, we see powerful echoes of themes—forgiveness, belonging, and the complexity of social roles—that resonate deeply in any age. This small letter sheds light on what it means to embrace humanity beyond titles and status.