Why take a body? Why make a Ring?

[Raynor]

I am not sure about Melkor's greatest gift being his capacity to learn (well, he could have it, but he forgot about it ); he gave less heed to the information Eru gave about the Eruhini than even Sauron ; he also failed to see that he can't fight against Eru, even after he is so warned by Eru himself. Oh well - at least His words assure us that even Melkor _will_ see he was only a tool for greater beauty.

I wonder how is it that the bad guys haven't noticed all those things in the Ainulindale which foretold the failure of evil (by and large - or at least that of Melkor in his direct and immediate quest). Melkor himself was too caught up with his own makings; Sauron may have noticed the writtings on the wall, but he later became enamoured of Melkor's power to bring about his plans of organising; perhaps all the rest were from the begining swayed by Melkor and noticed and remember very little.

That must tell us that somehow, the One Ring worked by enabling the wearer to 'see' those who wore other Rings

Apparently, even Frodo is able, theoretically (?), to do such a thing with the one ring:

Originally Posted by The mirror of Galadriel, FotR

- I am permitted to wear the One Ring: why cannot I see all the others and know the thoughts of those that wear them?

-You have not tried, she said.

the Ring, crafted with words, enabled Sauron to break down the barriers of Unwill?

Interestingly enough, one's unwill may not always work as expected, as we see in the case of Saruman with the palantir:

Originally Posted by The Palantir, TTT

But Saruman certainly looked in the Stone since the orc-raid, and more of his secret thought, I do not doubt, has been read than he intended.