Philemon

Philemon actually is anti slavery. Jewish Law forbids returning an escaped slave to their owner, so Paul in effect restores Onesimus to freedom, and demonstrates Jewish Law is no more binding, but rather the Spirit of Grace, by returning him as a freed man and not as a slave. It demonstrates how Grace is not by the letter, but through the Spirit. And then Paul restores all his owed debts, demonstrating how Christ saves us even more. Onesimus actually becomes a pretty significant person in the early church, too.