I realized what this was as soon as I started reading it lol, I've read it before. But it is absolutely fascinating to me every single time. 
 I believe in the idea that, some day, time travel will be real, which means it is probably happening right now. And I believe in the idea that some people are reincarnated over and over again to live out lives during different eras of time--how can they not? A lot of people believe in the afterlife and perhaps there is one. Perhaps some people DO go to Heaven or Hell or get trapped on Earth as a spirit, but not everyone does. How could that be possible? If Heaven is real then that means it has to exist somewhere in a place that takes up space, even if it's in a realm that we, as living humans, cannot see. That means that, if it takes up space, it will fill up and become full eventually--the same thing goes for Hell, if there is one. The amount of humans that have lived and died since humanity began is countless so how can everyone fit in two or three places with limited space? Especially when you take into consideration how many people die daily. There HAVE to be some souls that are set for reincarnation. Perhaps it's the same souls over and over again, but perhaps not. Perhaps the author is right and we are just one living, breathing entity and WE are the universe. That theory fucks me up a little more than my own, but it WOULD explain how countless amounts of souls are able to coexist within just three realms. 
 I just, I dunno man. I love this story so much though. I find it absolutely fascinating.