Actually, Eru shows the Ainur a vision of what their music was about, and because they were all interested in it enough, Eru made it so, and Eä came into being. Eru was the only one who could give Life (the "secret fire" occasionally mentioned) to things, which is what Melkor/Morgoth most envied. Being the Satan figure is always rough.
JRRT was a rather staunch Catholic, and kept to the "almighty, maker of heaven & earth" line even in his great work of fantasy.
And to go back and pick a nit that Aslan brought up earlier, Sauron DOES in fact take on physical form at the end of the Third Age. There is a passage in the Two Towers (haven't the time to look it up precisely) where Frodo is talking about how Isildur cut the One Ring off of Sauron's hand. Gollum replies that there are only four fingers on the "black hand, but they are enough." Keeping in mind that Gollum was personally ... questioned ... by Sauron about that Baggins character, and that sounds like an eyewitness account to me.
Right, I'll stop niggling about the details now.
-Chris Landmark
(Don't hold me to that promise...)
"Was entstanden ist, das muss vergehen. Was vergangen, auferstehn." -Klopstock & Mahler
"Only liberals really think. Only liberals are intellectual. Only liberals understand the needs of their fellows." How much viciousness lay concealed in that word! Odrade thought. How much secret ego demanding to feel superior. - Heretics of Dune