A cursory reading of Ephesians 6:5 has left some with the impression that the Bible condones slavery. The introduction to this message ("Our Work and Our Character") by Timothy J. Keller of Redeemer Presbyterian Church in New York City provides some great historical context crucial to understanding what Paul is actually saying in this passage.
Keller points out that we're on the other side of slavery in the western world that inevitably influences how we understand that word. But the slavery referred to in the Bible was a fundamentally different practice. Some translations try to indicate this by using the word "bondservant."
Biblical "slavery" was not race-based. It wasn't motivated by racism. It wasn't kidnapping and selling, treating human beings as property. Most "slaves" at that time were captives from war; others voluntarily became slaves to pay off debts. Neither were permanent situations. Freedom was an almost inevitable outcome for "slaves."
Further, in the Greco-Roman world, slaves had rights. They were not property. Slaves could appeal to the magistrate if their rights were violated. There were laws governing how they were to be treated.
That's not to say the practice of slavery in Biblical times was good or easy. It's simply not the same as what we think of. It's important to understand Paul in an accurate historical context. He doesn't condone slavery, i.e. capturing and owning people as property.
Keller points out that Paul is not condoning any cultural practice, but instructing Christians how to lead God-pleasing lives in the world they found themselves in. Paul's teaching doesn't condone any form of slavery. His purpose in this passage isn't cultural revolution, but personal revolution under the Lordship of Jesus Christ. And what Paul teaches about respecting one another sowed the seeds for cultural change.
The Bible doesn't condone slavery. The historical institution was radically different than what was practiced in the western world. Paul's goal was personal conduct, not cultural change. And what the Bible teaches about human beings would eventually lead to cultural change. The abolitionists of the last centuries applied what the Bible teaches about human beings to bring about the eradication of an evil practice.