The Inherent Incompatability of Morgoth and Sauron

[Zigûr]

Originally Posted by Sarumian

The fact Sauron could delude himself this way means that he had/obtained a very wrong idea of Eru. Not only Eru's motives and attitudes but of Eru's nature. He thought about Eru as if the latter was somewhat a first among Ainur, not an ultramundane spirit, having all of the universe, Ainur including, existing in his mind.

I think the point is that Sauron assumed Eru no longer cared, not that he thought that Eru's power was in any way limited. Sauron knew Eru's power. He simply did not know his mind, but nonetheless made assumptions about it. As Professor Tolkien states in 'Notes on motives in the Silmarillion', "Sauron was not a 'sincere' atheist, but he preached atheism, because it weakened resistance to himself (and he had ceased to fear God's action in Arda)." I don't think Sauron had any doubts about what Eru could do, but he made a number of assumptions about what Eru would do, and not necessarily large ones given how uninvolved Eru apparently was.