Looking at the relevant passages it is clear that the Bible does indeed endorse slavery.
In the Old Testament God approved the practice and laid down rules for buyers and sellers (Exodus 21:1-11, Leviticus ).
The Christian Roman Empire actively helped slave owners to recover fugitive slaves, and punished anyone giving them shelter. In 650 Pope Martin I condemned anyone teaching slaves about freedom or encouraging them to escape their bonds.
A Church Council of Châlons in 813 decreed that slaves belonging to different owners could not marry without their owners' consent.
Christians had no doubt that it was divinely sanctioned, and they used a number of Old and New Testament quotations to prove their case.
Soon the Church would become the largest slave owner in the Roman Empire.
Bishops themselves owned slaves and accepted the usual conventions. Slave collars dating from around AD 500 have been found in Sardinia, stamped with the sign of the cross. "I am a slave of Felix the archdeacon: hold me lest I run away".
Men are at liberty to sell their own daughters (Exodus 21:7). It is acceptable to beat slaves, since they are property a master who beats his slave to death is not to be punished as long as the slave stays alive for a day or two, as the loss of the master's property is punishment enough: And if a man smite his servant, or his maid, with a rod, and he die under his hand; he shall be surely punished.
Notwithstanding, if he continue a day or two, he shall not be punished: for he is his money.