Slave trade owners pointed to the existence of slavery in the Bible as justification for the institution. Traders and owners claimed that slaves were being exposed to Christianity.
In the colonies, Churches accepted slavery as normal. Where priests raised concerns from the pulpit, life was made difficult for them.
Owners claimed the bible supported the existing structure of society. For example St Paul's instructions to servants about obedience to masters.
There are many examples of slavery in the bible and the bible does not state that slavery is wrong. Racial theories such as 'the curse of Ham' grew popular in the 1700s. Ham is a son of Noah (of the Ark). The story says he was cursed for his sins and his skin turned black. The myth continues that Africans were the descendants of Ham who are punished for Ham's sins.
It is also difficult to read the bible without condemning the behaviour of slave owners. The duty of converting slaves to Christianity raised the implication of teaching them to read so they could study the bible. These problems were ignored.