As stated, slavery was a fact of the Ancient World, and so when the Bible addresses the topic, it should not be compared against the sensibilities of the modern world, but rather against the sensibilities of the ones to whom the Bible was addressed.
It is an anchronism to apply questions of, for example, feminism or communism, to the Scriptures, because the original audience would have had no means of apprehending it as such. It would have made no sense, for example, to put an apologetic against evolution into Genesis, because until the 1860s, no one had ever conceived of the notion. Likewise, to rail against the evils of slavery would not have made sense to the original audience.
What was the status Quo on Slavery?
As Nelson's New Illustrated Bible Dictionary puts it:
People could become slaves in several ways. The poor who were unable to pay their debts could offer themselves as slaves (Ex. 21:2–6; Neh. 5:1–5). A thief who could not repay what he had stolen could also be sold as a slave. Children born of slave parents became “house-born slaves” (Gen. 15:3; 17:12–13). Sometimes children would be taken as slaves in payment for debts (2 Kin. 4:1–7).
What did the Bible teach?
That said, when Scipture is compared to prevailing attitudes, Scripture is remarkably anti-Slavery in comparison.
The laws concerning the treatment of slaves were remarkably liberal:
a. Israel was instructed by the law not to rule over a fellow Israelite harshly (Lev. 25:39; Deut. 15:14).
b. If a master beat a slave or harmed him, the law provided that the slave could go free (Ex. 21:26–27); and the killing of a slave called for a penalty (Ex. 21:20).
c. Slaves were allowed to secure their freedom. Under the law, no Hebrew was to be the permanent slave of another Hebrew. After six years of service, a slave was to be released (Ex. 21:2; Deut. 15:12).
d. In the Year of JUBILEE, no matter how long a slave had served, he was to be released (Lev. 25:37–43). If a slave desired to continue with his master, he would have a mark made in the ear; this mark would signify that he had chosen to remain a slave (Ex. 21:5–6).
e.A slave could also buy his freedom, or another person could buy his freedom for him (Lev. 25:47–49).
N.B. In fairness, there is no evidence that the Hebrews ever actually did the Jubilee, but it is instructive that the concept was embedded both in the Law and the Prophets. Additionally, the fact that it was never practiced shows how radically out of step with the time it was.
- The prophets are remarkably on the side of the slave and against the master.
The Bible contains warnings about the practice of slavery. The prophet Amos spoke woe to Gaza and Tyre for their practices of slave-trading entire populations (Amos 1:6–9). The Book of Revelation declares that disaster awaits those who sell slaves (Rev.18:13). ... Paul appealed to Philemon to receive back Onesimus, a runaway slave who was now a Christian and therefore a brother (Philem. 1:16). Elsewhere Paul counseled believing slaves to seek freedom if they could (1 Cor. 7:21). Since slave practices were part of the culture in biblical times, the Bible contains no direct call to abolish slavery. But the implications of the gospel, especially the ethic of love, stand in opposition to slavery.
Additionally, Paul is as clear as you can get that there should be no difference between slave and free:
Galatians 3:28 says:
There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus.
The Good News of the Kingdom of God in Isaiah is that Jubilee (Lev 25:37) would actually come about. Mary is also equally clear that she thinks the tables are going to be turned, and the "oppressed" would be free.
What was actual practice?
I'm not going sugar-coat Christian history. Whites treated Blacks horrendously. The AME Church was founded by a black minister who was savagely beaten at the altar of St. George's Church. Slave masters often tried to stress the value of obedience amongst slaves. Theological cases (like Ham in Genesis 10) were often made to to try to say taht the white man was superior.
But interestingly, it was still within the church that opposition to slavery was at its greatest.
William Wilberforce and John Newton are widely credited with the abolition of slavery in Great Britain, and the ban in 1808 on the trading of slaves. Both unashamedly said their opposition to slavery was born out of their understanding of Christianity.
The Quakers were remarkably opposed to the subjagation of people - their refusal to simply take land from the Indians to their united opposition to slavery was a constant force in the abolitionist movement.
Finally, from Rev. Dr. Martin Luther King to the Southern Christian Leadership Conference to even the Reverend Jesse Jackson - most of the stalwarts of the Civil Rights movement were leaders in the Christain Church.
What did the rest of the world believe?
In contrast,
While slavery was practiced worldwide, the Christian church was the first to react heavily against it. It was the Christian church that first abolished and then "forced" that view on many of what I freely admit were its subjagted colonies. Still, the point is this - it is not natural to set your property free. It takes something engrained in a society to make it change, a "religion" of freedom, and Christianity seems that most likely force.