Albert J. Raboteau explains why the colonies needed moral justification for their actions.
The economic reasons for the enslavement of Africans were the overpowering reason underlying the Christian justification. The need for slave labour, particularly on the plantations that developed in the Southern colonies, was at the heart of the slave empire in terms of cotton, in terms of indigo, in terms of other crops. Cotton being the major one, and as the Southern colonial regions spread westward, it became all the more powerful. And this is not just true of the North American colonies, which really were small potatoes originally in terms of the enslavement of Africans. It was true in the Caribbean, and was true in Brazil. Indeed, slavery didn’t end in Brazil until the 1880s.