Does God condone slavery? Absolutely not! It was NEVER His intention for anyone to own another human being. What does the Bible teach about slavery? The Bible teaches to have compassion for slaves.
God gave laws concerning slaves because of man's depravity. The laws of Moses were introduced at a time when it was common to own slaves. Even Abraham, the father of faith, owned slaves. He was not chosen by God because he was a perfectly righteous man; he was chosen because of his faith in God's goodness and His promise of redemption of the soul through the Messiah.
God patiently bore with Abraham's depravity, his slave–owning, his lying, and other sins, because Abraham wanted to be in relationship with God and overcome his depravity. It was an ongoing process of perfection that, in Abraham's lifetime, did not entirely do away with his slave ownership. He was headed in the right direction, though, in regards to building character.
When a person has complete control over another person's life, it can lead, for many, to behaving unspeakably depraved towards the slave. God knew that people who owned slaves were not likely to instantly give them up, but if He could, at least, get them to behave more decently towards them, it would be progress, and the natural outcome of going in that direction would be the slave owner's eventual realization that they had no business making slaves of other people in the first place.
This was indeed the outcome in the western world where Christianity gained a foothold. Most of the abolitionists who worked to make slavery illegal were Christians. It was not Christianity that kept slavery in place, while it lasted, though some Christians were involved in that. It was the IMMATURITY and CARNALITY of those Christians that caused them to support slavery, not their Christianity. They were Christians who did not yet see the wrongness of owning slaves, but they were convicted that they should take good care of their slaves and not use them sexually or be too hard on them in regards to physical punishment. It definitely was better for a slave to be owned by a person with a conscience, even if it was not a well–developed conscience, than for them to be owned by someone who had very weak brakes on their depravity.
Jesus taught for us to do unto others as we would have them do unto us, and nobody in their right mind wants to be made into a slave. The Golden Rule overrules any right that people think that they have in regards to owning slaves.
The Apostle Paul gave instructions concerning slaves to mitigate a grievous situation. He told Christians who owned slaves to treat them according to a certain level of consideration, and he gave instructions to slaves that would help keep them out of trouble while they were in bondage. He encouraged them to get out of slavery, though, if they could. He said what he could say about the subject without getting the authorities that ruled at that time so riled that it would result in more intense persecution of Christians because of their higher views of justice.
Anyone who thinks that the Bible condones slavery has a very immature understanding of the Scriptures.
Your word have I hid in my heart, that I might not sin against you.