In the book of Philemon, what is the underlying theological implication of Paul urging Philemon to receive Onesimus back, not as a slave, but as a brother?

A Paul was primarily concerned with maintaining social order and the institution of slavery. B Paul was attempting to undermine the Roman economy by encouraging slaves to rebel. C Paul was demonstrating that Christian fellowship transcends social hierarchies and that all believers are equal in Christ. D Paul was simply trying to avoid conflict between Philemon and Onesimus.