Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
This is not a funny story, and the narrator takes his task to educate the reader about the horrors of slavery very seriously indeed. He frequently makes comments intended to enlighten us about the moral conclusions we should draw from its events and to remind us that, even if a character feels alone or abandoned, God is with him. There is also a clear reminder, provided over and over, that judgment is coming, and if we wish to avoid it, we must do what is right.