It seems whenever the question of slavery and the Bible comes up, everybody starts to get their fundie on. Even people usually far-removed from the fundamentalist and evangelical subcultures start using some of its more dubious tools — like the vivisection-by-concordance approach to Bible study. Yes, concordances are helpful, and this can be a fruitful approach, but only if studying the index is not seen as the equivalent of, or a substitute for, reading the book.
In this case, actually, you'd be better served by reading the Table of Contents than by reading the index: "Genesis, Exodus, Leviticus, Num …"
Wait, what was that second one?
Right, Exodus. The title of that book is the first and last biblical word on the subject of slavery.
Exodus definitively establishes the motif and the trajectory. Liberation starts here. But it does not end here.
The Exodus story provides refrains that echo all through scripture: "You were once slaves in Egypt," "the Lord brought you out of slavery in Egypt." This refrain is the basis for much that follows in the law and the prophets. You were once slaves in Egypt, so we're going to practice liberation every Sabbath year and every Jubilee. You were once slaves in Egypt, so breaking every yoke is what religion is all about. And further along this trajectory, You were once slaves in Egypt but I brought you out, so you're going to love your neighbor and even love your enemies.
The Exodus is, to borrow an image from Buddhism, a finger pointing at the moon. Measuring the length and the limits of that finger misses the, well, point. Woolman and Wilberforce understood this. Martin Luther King Jr. understood this. Bob Marley understood this.
So if you've an interest in this subject — what the Bible says about slavery — you need to do more than study the finger. You need to look where it's pointing.