Throughout Philemon, Paul uses several key terms in relation to the dispute between Onesimus and the household (Philemon, Apphia, Archippus and all who meet in their home). Chief among these is the nouns δέσμιος (“prisoner”) and δεσμοῖς (“chains”), used in vv.1, 9-10 and 12, where the first use of the term is directly self-applied: Paul calls himself a δέσμιος Χριστοῦ Ἰησοῦ in v.1 ("prisoner of Christ Jesus") and again in v.9. The significance of the epistolary opening (here vv.1-3) is that Paul has set the stage with a rhetorically fascinating move by applying the noun of subjection to himself.
This self-designation (along with δοῦλος: “slave”) is not uncommon in the introduction of Paul’s epistles (c.f. Rom. 1:1; Phil. 1:1; Eph. 3:1) and in the subsequent Pauline tradition (Tit. 1:1). Here, however, the term δέσμιος has a more nuanced and rhetorically powerful range. But first, allow me to paint the picture.
The social context of Philemon is notoriously complex, as if one has dimly lit a big stage. Any struggle to see the various moving parts and additional stagehands and actors automatically makes it difficult to piece together a coherent reason for this epistle. However, it is my contention that Onesimus is not a runaway slave, but is more likely an emissary of this house church, being sent away (perhaps as a ‘useless’ slave; see v.20) by them to serve Paul in some temporary capacity. While the concept of “owing” (v.18; ὀφείλει) may refer to a fiscal or legal debt (though this is doubtful), it seems more probable that this ‘debt’ Onesimus has refers to the problem of simply being a slave in the ancient world, with all the duties and expectations that follow. The use of the conjunctive particle εἰ in vv.17-18 (“if”) also lessens the need for certitude regarding Onesimus’ runaway status.
Paul, by sending back this slave—presumably with this actual epistle for the household, a canonized book of the New Testament—has within a single word undermined the sovereignty of the household. Identifying himself as δέσμιος is a blatant characterization of himself with slave status, particularly a higher master all within the household know: Christ Jesus. By this, Paul is appealing to a higher power, just to cover his bases. Paul is himself captive to Christ in the same way Onesimus was captive to the household, even in obligation.
In order to stress continuity between him and the slave, Paul identifies Onesimus as his σπλάγχνα “(heart; inner seat of emotions” in v.7, 12, 20), showing the household that Onesimus is no longer a slave (assuming Paul believed that Onesimus was a slave from the beginning, which seems doubtful), but is instead a ἀδελφὸν ἀγαπητόν (“beloved brother”). The power of Paul’s rhetoric is the undermining of the status of Onesimus as slave by identifying himself with Onesimus, and identifying Onesimus as himself. Instead of sending Onesimus off to be brutalized or possibly kept in harsh work, Paul performs something like a synecdoche. Paul’s subsequent referral of himself as πρεσβύτης (“old man”) suggests a firm and wise adage: honor those older than yourself.
How could the household refuse Paul, especially with this language of kinship, as a prisoner of Christ?
How could they take Paul’s statement about “no longer as a slave” as anything else?
Onesimus, then, is no longer a prisoner but a member of God’s family. Where Onesimus had little voice or moral agency in the world as a slave, Paul took it upon himself to both identify with him and speak up for the one who had no voice or status. Paul affirmed Onesimus' moral and cognitive agency by using the bodily image of “emotions” to communicate that he stands as Onesimus (v.20).
Because of Paul’s rhetoric on Onesimus’ behalf, as his advocate, it is highly likely Onesimus was granted manumission and continued to serve with Paul in the Gospel (Col. 4:9). This of course depends on the dating and authorship of Colossians (I do think Paul wrote Colossians, and Philemon is more likely to have been written first) Sometimes, it is the little things, the words we speak on behalf of others that make all of the difference.
What a marvelous epistle.