This is a great read from The Public Domain Review. I asked my best friend this and now I'll ask you all: What three books would you recommend Frankenstein's Monster to read to better understand humanity?
https://publicdomainreview.org/collection/frankenstein-monster-reading-list/
When having the discussion with my friend, her choices centered around explaining the actions of humans/human nature, so my personal choices follow suit:
1. Sophie's Choice, because sometimes people are put in situations were they have no choice but to do horrible things.
2. Utilitarianism By John Stuart Mill, to explain that sometimes people do bad things because it hurts the least or the good it does out weights the bad.
3. Mencius. This one is going to take a bit of explaining...
So I chose Mencius not for the text as a whole, but there are two key stories in it I think are illuminating.
1. The Story of the Cow. There was a new ceremonial bell and to consecrate it, the king was to sacrifice a cow, but when he saw the cow, the cow looked scared so he took pity on it and ordered a random goat be used instead. The people thought he was cheap, but it was really an act of compassion.
The moral we can't know a person's intentions...
2. The example of a child near a well.
Mencius explains that a complete stranger can see a child playing near a well and will feel uneasy about it due tot he danger of the child falling in, despite not knowing the child, their parents, etc, and because of this Mencius argues that people are of a good nature.
And it is because of these two passages that I recommend Mencius.