In the Very Beginning
While scientists observe that the universe is a sufficient cause in of itself - and that proposing God as its cause has no additional explanatory benefit - I will presume to take one step back.
In the primitive origins of reality, there was simply chaos. The domain of personality - of timeless resonances - was able only to locally impose order upon the domain of structure. The resonances were sustained by the possession of structure, making structure an object of competitive struggle. Personalities absorbed each other through struggle, building larger structures. Not infrequently, however, struggle resulted in the destruction of personality. Ultimately, it became clear that the only way to end the threat of destruction was to accept complete unification.
In the realm of God, each personality accepted a role in exchange for eternal life. It was understood that failure to accept this contract would lead to dissolution and destruction. If lesser personalities refused to support higher personalities, they faced the threat of consumption. If higher personalities took an independent direction, they abdicated the claim of authority over their components, and faced rebellion.
Inevitably, however, as the memory of disorder faded, there would be those who would rebel against the contract. Why should they not have the right to construct their own domain, particularly if they had associates that wished to participate along with them?
The reason, of course, was that any such contract was unstable. Allow alternative realms to develop, and enter the possibility of competition. Once war begins, the contract is unsustainable at the edge of the domains: lesser personalities will be destroyed. If that contract is not maintained, the entire structure unravels.
So the only possible method for change is a coup d'etat. This is the story of Lucifer and the Fallen.