I think we have to go even further back than to Amun and the powerstruggles at Waset (Gr: Thebes) when talking about this.

In the dawn of Man´s era on earth, as he was influenced by his surroundings he had a need to explain them to make life understood and survival possible. Out of this came the early myths of creation, the tales of how deities created the land, the waters, the skies, the animals etc, etc., not to mention the movements of the sun and the moon and other powerful natural phenomena. And as these things were superior to Man, he put it up to Powerful Beings/Gods behind it. Existence was granted by these beings, and Man lived according to these stipulated conditions. So to gain an amount of influence over survival, luck in hunting, in harvest, in protection against enemies etc, Man supplicated the deities, offered to them in order to make them beneficial and helpful to his purpopses.

Soon, alongside of the development of civilisation, Man developed a religious system of handling the interaction with the Heavenly Realm. And it seems that those who were most successful in hunting and in defending the community had the favours of the deities and so was the natural leader of the tribe. This is how the theocratical state of Egypt might have developed. Power lay in the hands of the gods and it shifted as eartly power shifted. If you were conquered in a battle, the gods had given the power to your conqueror or even shifted power between themselves.

The gods were many and varied from tribe to tribe. A conquering chief and his family made sure to incorporate the local deities/pantheon of the conquered people into his own or simply obliterate it, thereby proving that his own deity was the more powerful. This could be one of the underlying reasons for the different creation myths - it seems for example that the Memphite Theology was 'invented' by the priesthood as an effort to undermine the Heliopolitan Creation Myth.

Although it would not be correct to call these powerstruggles totally political. What we often forget when looking at ancient Egypt, is that it was a theocracy, where what we today call 'religion', was a non-existing word. There was simply no difference between religion and politics, it was the same thing. Pharaoh was literally the Living God and he was the total ruler of everything and everyone. So what happened at the temples and among the upper echelon priesthood (who more often than not were relatives and friends of the ruling family) it was to legitimize and secure the throne of the King and his rule - because The King and his rule was the same as the temple. The King was the first priest of them all in the land, he was the link between the people and the gods, himself a Living God at the same time as a human being. So to legitimize him, the god was also legitimized and vice versa. Heavenly power was equal to Earthly power which in essence meant that the gods ruled Egypt through Pharao. This all happened on a state level, with little or no consideration of what people would think or say, private religion on the level of the commoners was another matter.