I hypothesize that gods and spirits do not exist outside of the body, but exist as purely as memetic beings. This would explain how one person can summon a god such as Amon, while another is summoning the demon Amon. It is a simple interpretation of data, and much like how computer can perform different actions with very similar code, so does our brain.
Amon was given worship in ancient Egypt over a period of several thousand years, and developed into a deity type that was significantly different from its origin.
In the most ancient of times, Amon was a being kept in a dark cavern, a terrifying draconic figure to whom virgins were offered as sacrifices.
Over time, the beast in the cave was replaced by a idol in the form of a man made of solid gold, and the sacrificial virgins were replaced by priestesses who would descend into the shadows to copulate with the cold embrace of the original handsome dark stranger.
The sexual nature of the role and its eventual development into a more important deity led the development of the concept of Amon to more typical fertility motifs like the ram's head with which it is now most commonly identified.
If you were to take a person from later Egypt and transplant them into early Egypt, they would be utterly shocked and bewildered by some of their own deities under their older forms. A modern audience has even less of an understanding of the deities, and we are often given prejudices that delineate between gods and devils which the ancient people did not always share.