Quote 37
Sunday was my only leisure time. I spent this in a sort of beast-like stupor, between sleep and wake, under some large tree. At times I would rise up, a flash of energetic freedom would dart through my soul, accompanied with a faint beam of hope, that flickered for a moment, and then vanished. I sank down again, mourning over my wretched condition. I was sometimes prompted to take my life, and that of Covey, but was prevented by a combination of hope and fear. My sufferings on this plantation seem now like a dream rather than a stern reality. (10.6)
It's a small thing, but Douglass is talking about what a beast he's become and what an animal Covey has turned him into on Sunday. Southerners often defended slavery by talking about how they were bringing Christianity to slaves, but Douglass (who is a dedicated Christian) wants to show that the opposite is true.
Quote 38
I assert most unhesitatingly, that the religion of the south is a mere covering for the most horrid crimes,--a justifier of the most appalling barbarity,--a sanctifier of the most hateful frauds,--and a dark shelter under, which the darkest, foulest, grossest, and most infernal deeds of slaveholders find the strongest protection. Were I to be again reduced to the chains of slavery, next to that enslavement, I should regard being the slave of a religious master the greatest calamity that could befall me. For of all slaveholders 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. (10.19)
Truth: Douglass got in some trouble for attacking the hypocrisy of Christians in the South, but he never backed away from that attack. Since his friends in the abolitionist movement were Christians, too, some of them thought he was attacking them instead of religious imposters. This passage tries to clarify the issue, explaining that his harsh criticism was not of all religion, but only for slave owners who pretended to be Christians, since it was impossible to be a true Christian and also own slaves. (In fact, he wrote the entire appendix just to explain that he was against hypocrites, not religion itself.)
Quote 39
I find, since reading over the foregoing Narrative, that I have, in several instances, spoken in such a tone and manner, respecting religion, as may possibly lead those unacquainted with my religious views to suppose me an opponent of all religion. To remove the liability of such misapprehension, I deem it proper to append the following brief explanation. 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. I love the pure, peaceable, and impartial Christianity of Christ: I therefore hate the corrupt, slaveholding, women-whipping, cradle-plundering, partial and hypocritical Christianity of this land. (Appendix.1)
Douglass wants to be completely clear that he isn't against religion or Christianity in general: he's just against the kind of religion that justifies slavery. In fact, he also doesn't believe that "the slaveholding religion" is a religion at all.