It's all just souls, the age of the soul and the intentions of the soul combined with the perception bias of the observer is what creates the differentiation's when it comes to defining what's what.

There are good souls and there are bad souls, there are young souls and there are OLD souls.

A good and old soul is the most likely to be perceived as a deity or an angel or something similar while an old and rotten soul is the origin of the whole demon mythos, they will lie and do whatever it takes to get a foot in the door because they are limited (by others) so have to be let in willingly(they are basically recruiting for their side).

Looking at it with this in mind and you will see that a lot of things all of a sudden start to make all kind's of sense...