[Belegorn]

In his desire to enter the world Melkor wanted "to be a master over other wills." [Sil, p. 8] Aulë is really the contrast to Melkor; "Melkor was jealous of him, for Aulë was most like himself in thought and in powers" [p.20] although "In the powers and knowledge of all the other Valar he had a part" [p. 25] He went from wanting to make things others had not thought of, to making "nothing save in mockery of the thought of others" [p. 20]. Aulë longed for the coming of the COI so that he could be their teacher which was his impetous for creating the Dwarves. Melkor on the other hand wished "to be a master over other wills." When Illuvatar questions him about his motives and how the Dwarves would be automatons under Aulë he says, "I did not desire such lordship" [p. 40] which shows to me that his thought to lesser creatures was in no way like that of Melkor's as you will see clearly if you continue reading the passage. He even says he did not mean to make the Dwarves in mockery of the vision of the COI, like Melkor had done in making things in mockery of the other Valar. I would say Eru rebuked Aulë because he had not given him that power to create life, "Why dost thou attempt a thing which thou knowest is beyond thy power and thy authority?" [p. 40] Aulë thought to destroy the Dwarves because he felt it was an offensive action, "and in my impatience I have fallen into folly" [p. 41] You ask why Eru spared the Dwarves, the text says, "because of his ( Aulë's ) humility". [p.41] He then made them a part of his plan unaltered as Aulë had them made.