Examining the character of Onesimus in Philemon, what central theme of Paul's letter is most directly exemplified by Onesimus' transformation and Paul's appeal to Philemon?

A The importance of maintaining social hierarchies within the early Christian community. B The transformative power of the Gospel to reconcile individuals across social barriers and redefine relationships. C The necessity of strict adherence to Roman law within Christian communities. D The economic benefits of converting slaves to Christianity.