How we cite our quotes: (Chapter.Page)
Quote #4
A master might kill his slave for nothing—for mere spite, malice, or to pass the time. (18.4)
This is like the idea of not being able to leave without permission. Twain puts his finger on a key part of what slavery is here: a life that the law considers worthless.
Quote #5
They had been heritors and subjects of cruelty and outrage so long that nothing could have startled them but a kindness. (19.4)
This could suggest a workday normality to slavery and oppression. Everyone's used to it, so they don't realize how wrong it is, and this reality puts Hank's task into stark relief. It's not enough for him to free everyone: he has to get the whole society to accept it and treat each other differently as a result.
Quote #6
One needs but to hear an aristocrat speak of the classes that are below him to recognize—and in but indifferently modified measure—the very air and tone of the actual slaveholder. (25.2)
This passage gets at the heart of the issue: Why, specifically, does slavery exist? Because some people think they're better than others. It's sad, but it happens time and again throughout human history. It's still around today, which just might be why people keep reading books like this one.