How does one understand the nature of humanity? Is it something defined for us, or something that we must invent? What are the implications of either decision?

Before understanding the nature of humanity, you would have to find your own definition of what it is to be "Human" or what you would describe as being "normal" in your own terms. It's not clearly defined or invented but something to decide on your own. You can agree with somone elses idea of what it is to be "Human" or you can find your own. The implication that can be taken from this is also something to decide on. You can have your own implication of why you should have your own answer of what it is to be "human" and why it impacts you.

these are the choices

local priests

european monarchs

common people

bible translators