In the book of Philemon, what underlying principle of Christian fellowship and reconciliation does Paul subtly advocate for regarding Onesimus, the runaway slave?

A That Philemon should publicly denounce Onesimus as an example to other slaves. B That Onesimus should be sold to another owner in a distant location to avoid further conflict. C That Philemon should free Onesimus and receive him back not as a slave, but as a beloved brother in Christ. D That Onesimus should be punished according to Roman law to maintain social order.