:Is evil but a part of Ilúvatar symbolised by Melkor? is its purpose to achieve balance between good and evil (well to engage in a struggle with good for supremacy and thus be a catalyst for good to rise to greater good)? Is it merely created to avoid a neutral grey mass?:

I found a passage where Tolkien addresses this:

"He [Manwe] must have grasped with great clarity what even we may perceive dimly: that it was the essential mode of the process of 'history' in Arda that evil should constantly arise, and that out of it new good should constantly come. One especial aspect of this is the strange way in which the evils of the Marrer, or his inheritors, are turned into weapons against evil. If we consider the situation after the escape of Morgoth and the reestablishment of his abode in Middle Earth, we see that the heroic Noldor were the best possible weapon with which to keep morgoth at bay, virtually beseiged, and at any rate fully occupied, on the northern fringe of Middle-earth, without provoking him to a frenzy of nihilistic destruction. " (Morgoth's Ring pg 402)

Russ