In Chapter 1, Douglass alludes to a common biblical justification for the institution of slavery. He uses logos to dismantle this justification:
If the lineal descendants of Ham are alone to be scripturally enslaved, it is certain that slavery at the south must soon become unscriptural; for thousands are ushered into the world, annually, who, like myself, owe their existence to white fathers, and those fathers most frequently their own masters.
In the Bible, Ham is one of the sons of Noah. One night, Noah gets drunk and falls asleep naked. Ham walks in and sees his father naked, then tells his brothers about it. His brothers cover up their father and carefully avoid looking at him. When they tell Noah later about what happened, he curses Ham's son, Canaan. While his two other sons and their "brethren" will be blessed by God, Noah proclaims, Canaan and his "brethren" will serve them.
Historically, apologists for the institution of slavery claimed that Black people were the descendants of Ham and were divinely ordained to serve white people. This is a convenient excuse for a racist practice, but Douglass accepts for a moment that this claim is true. He argues that if this is the case, the "scriptural" justification for slavery is about to fall apart. He has just described how white men, like his presumed father, are incentivized to sexually assault enslaved women. Children born to enslaved mothers would also be legally enslaved, so sexual assault allowed white men to increase their wealth in the form of human chattel. Here, Douglass suggests that the regularity of this practice is breaking down racial categories. He takes himself as an example. He has both Black and white ancestry, so there is no way to say whether he is "scripturally" cursed with enslavement or blessed by God to be served by Ham's descendants. There can no longer be a functional curse of Ham if everyone can draw an ancestral line to any one of Noah's sons.
Douglass does not necessarily believe in the Curse of Ham to begin with, but he is asking white readers to confront the holes in their own logic. He starts by agreeing with the general idea of the curse. He then demonstrates that racial categories are growing less distinct. By offering this new idea about race (new at least to many of his readers), he uses logos to convince readers that "slavery at the south must soon be unscriptural." By taking away the Bible as the moral basis for the institution of slavery, Douglass leaves white readers scrambling for another moral basis. That scramble itself reveals that no one was ever enslaving people because they thought it was God's will; rather, God's will was invoked as a convenient excuse.
In the Appendix, Douglass uses logos to clarify his position on Christianity and coax readers into reflection on their own hypocrisy:
What I have said respecting and against religion, I mean strictly to apply to the slaveholding religion of this land, and with no possible reference to Christianity proper; for, between the Christianity of this land, and the Christianity of Christ, I recognize the widest possible difference — so wide, that to receive the one as good, pure, and holy, is of necessity to reject the other as bad, corrupt, and wicked. To be the friend of the one, is of necessity to be the enemy of the other.
Douglass lays out a rubric that may be familiar to readers today: there is a difference between Christianity as itself and Christianity as an organized religion. This distinction was especially important to Black Americans in the 19th century (as it still is for many Black American Christians and other marginalized peoples practicing Christianity). A vast number of Black people were kidnapped by enslavers and forced to convert Christianity. Their descendants, too, were often raised Christian, both because these descendants' enslavers were Christian and because that was the religious tradition their family now had to pass down to them.
Christianity became a double-edged weapon in the battle between slavery and abolition. Douglass discusses a short-lived Sabbath school established by Mr. Wilson, where enslaved people were to be taught to read the New Testament. This school does not last long because other religious leaders throw sticks at the enslaved people to break up their meetings. This resistance to the Sabbath school seems to be because religious leaders on plantations were paid to pitch a version of Christianity that propped up the institution of slavery. For instance, they claimed that Black people were cursed by God to serve white people in perpetuity. Learning to read the Bible would allow enslaved people to practice their own Christianity, closer to the scriptural teachings, and question what religious leaders were telling them.
In this passage in the Appendix, Douglass offers readers new vocabulary to describe the perverted version of Christianity sold on plantations: "slaveholding religion," as opposed to "Christianity proper." By giving readers these new terms to think with, he allows readers to see the "slaveholding religion" not as a valid version of Christianity, but rather as its own separate "improper" system. People who see themselves as "good Christians" can thus not only agree with Douglass's critique without perceiving themselves to be blaspheming, but they can also reject as "unchristian" ideas that would align them with the "improper" system.