Douglass used the institution of Christianity to highlight the hypocrisy, brutality, and ultimately the corrupting influence of slavery. He creates a dichotomy of authentic and false Christianities, asserting that the brutality of slavery makes it incompatible with the faith. Throughout the book, he points out that many brutal, sadistic slaveowners and overseers are pious, God-fearing Christians on Sundays. This gap between their behavior and their affectations of Christianity makes the evils of slavery all the more stark. But Douglass goes even further, recognizing that slavery also, in a way, depends on this false Christianity, and indeed uses it as a prop. He notes that religious slaveholders are the worst of them all:
I should regard being the slave of a religious master the greatest calamity that could befall me. For of all slave-holders with whom I have ever met, religious slaveholders are the worst. I have ever found them the meanest and basest, the most cruel and cowardly, of all others.
Douglass explores the theme throughout the work, showing how the "religious shouts" of the evangelical Christian masters drowned out the "piteous cries" of his slaves. In this way, Christianity supplied a moral veneer to the lives of people who were implicated in an institution characterized by unspeakable brutality.