How does the apostle Paul's appeal to Philemon regarding Onesimus challenge the social norms and legal practices concerning slavery in the Roman world?

A Paul demands Philemon immediately emancipate all his slaves as a demonstration of Christian freedom. B Paul argues that Onesimus's conversion makes him legally equal to Philemon under Roman law. C Paul subtly advocates for a system of indentured servitude rather than outright slavery. D Paul appeals to Philemon's love and Christian principles to receive Onesimus back not just as a slave, but as a beloved brother in Christ, implicitly challenging the dehumanizing aspects of slavery.