A dominant theme is how a hierarchical structure can (or even if it should) exist within the body of Christ. The master/slave relationship was rarely seen as reciprocal though there may have been leeway as regards the rights of slaves (Gorman, 7-8). But, what I think we see is Paul’s pressing for Onesimus’s freedom. For instance, Paul’s strong and consistent use of “in Christ” applies here because Paul can claim that he is “bold enough in Christ to command you to do your duty,” thus seeming to imply that both master and slave are ‘in Christ’ and that Paul is as well: this is fitting as love is a grand Pauline theme (1 Cor. 13), and he consistently applies his principle here in a sensitive situation. Indeed, Paul’s claim for Philemon to “refresh my heart in Christ” may place the abolition of slavery directly within the freedom the Gospel offers (c.f. the “in Christ” language of Gal. 3:28). When there are no divisions within the body of Christ, we must then ask why the church attempts to perpetuate such division in—for example—excluding women from the pulpit, and why our individual churches do not include minorities in positions of equal standing in the Church.
The character of the Church (and Paul is writing to a church here! See v.1-2) is one of participation in unity, where there is no slave or free in Christ. Paul’s advocacy for Onesimus seems to open up a seat at the table of fellowship.