[Slavery in the Greco Roman cultures of the New Testament] is more like indentured servanthood. It's not what we think of as slavery. When you and I see the word "slave" in the Bible, you immediately think of 17th, 18th, and 19th century New World slavery: race-based, African slavery. When you do that, when you read it through those blinders, you aren't understanding what the Bible's teaching.

Historian Murray Harris … wrote a book about what slavery was like in the 1st century Greco-Roman world. He says that in Greco-Roman times, number one, slaves were not distinguishable from anyone else by race, speech, or clothing. They looked and lived like everyone else and were never segregated off from the rest of society in any way. Number two, slaves were more educated than their owners in many cases and many times held high managerial positions. Number three, from a financial standpoint, slaves made the same wages as free laborers and therefore were not themselves usually poor and often accrued enough personal capital to buy themselves out. Number four, very few persons were slaves for life in the first century. Most expected to be manumitted after about ten years or by their late thirties at the latest.

In contrast, New World slavery—17th, 18th, 19th century slavery—was race-based, and its default mode was slavery for life. Also, the African slave trade was [started] and resourced through kidnapping, which the Bible unconditionally condemns in 1 Timothy 1:9-11 and Deuteronomy 24:7. Therefore, while the early Christians, like Saint Paul … discouraged [1st century slavery] … saying to slaves, "get free if you can," [they] didn't go on a campaign to end it. [But] 18th and 19th century Christians, when faced with New World-style slavery, did work for its complete abolition, because it could not be squared in any way with biblical teaching.

So the point is that when you hear somebody say, "The Bible condones slavery," you say, "No it didn't—not the way you and I define 'slavery.' It's not talking about that."