In this post, I’ll enumerate a few more reasons why I believe that when Paul states that Philemon and Onesimus are adelphoi en sarki that he does not mean that they are both human beings.
Third, Paul notes that Philemon’s and Onesimus’s sharing “brotherhood in the flesh” is a relationship that goes beyond what Onesimus and Paul share. In some way, that is, Philemon and Onesimus are adelphoi en sarki in a way that Paul and Onesimus are not. Paul states that Onesimus is “a beloved brother, exceedingly to me, but how much more to you, both in the flesh and in the Lord.”
If Paul meant to note that Philemon and Onesimus share a common humanity, this would make little or no sense. All humans share in a common humanity. But if Philemon and Onesimus are adelphoi en sarki with this phrase meaning “actual brothers in the flesh,” then Paul’s words make good sense here. Onesimus would clearly be dearer and more beloved as a brother to Philemon than to Paul.
Fourth, Paul might have used other expressions if he were going to insist on the common humanity of Philemon and Onesimus. In Acts 10, Luke narrates the meeting between Peter and Cornelius, who falls on his face upon meeting Peter. Peter lifts him up and says, “I also am a man” (v. 26). I’ve already mentioned Seneca’s 47th letter, in which he claims that all humans “sprang from the same stock, [are] smiled upon by the same skies, and [are] on equal terms with [those who are free], each breathing, living, and dying.” Further, all humans “spring from the gods” equally. While other examples could be cited it is unlikely that if Paul meant to note their common humanity that he would assert that Philemon and Onesimus are adelphoi en sarki—“brothers in the flesh.”
Finally, if Paul really wanted to communicate that these two were blood brothers, what other expression could he have possibly used other than adelphoi en sarki? That they are “brothers in the flesh” is simply the plainest and most straightforward way of understanding this expression, even though it then functions as a serious thorn in the flesh for the majority view of the scenario lying behind Paul’s letter.
For tomorrow, a few alternative scenarios that can account for Paul’s language in v. 16.