Sarah's journey toward empathy is unique in that her society has rejected empathy towards slaves, for the most part. Many slave owners go to church with Sarah, but then they leave the religious institution and beat their slaves ruthlessly, commanding them to work difficult jobs for no pay, and Sarah watches. She starts to notice that her assumption that her community was automatically correct is wrong. She sees that the status quo is deeply broken and in fact, so wrong that it's hard to fathom it.
There is also the problem of explaining her awareness to others. The slave owners in Carolina have pseudo-logical arguments for why what they're doing is not evil or hypocritical. They have horrible ideas that are passed along through generational assumption, because children trust their parents so much by nature that it's hard to break the cycle of wrong belief. This question is underscored by Sarah's attendance at church. She wants to understand how people can believe that slavery is okay who also love Jesus and his message of equality, hope, and love, but there is no answer for this.
Eventually, she realizes that the answer is that white people have begun to believe a narrative about Black people that allows them to dehumanize them. Once they believe that Black people are just animals, then slavery doesn't feel evil anymore. This is blatant hypocrisy, says Sarah, because the religion that dominates the South seems specifically suited to reject slavery. Sarah realizes that the only hope that slaves have is political change, but this seems unlikely because of how much money people make by slavery.
