tolkienianos: tolkienianos: Melkor “incarnated himself” (as Morgoth) permanently. He di

tolkienianos:
Melkor “incarnated himself” (as Morgoth) permanently. He did this so as to control the hroa, the “flesh” or physical matter, of Arda. He attempted to identify himself with it. A vaster, and more perilous, procedure, though of similar sort to the operation of Sauron with the Rings. Thus, outside the Blessed Realm, all “matter” was likely to have a “Melkor ingredient”, and those who had bodies, nourished by the hora of Arda, had as it were a tendency, small or great, towards Melkor: they were none of them wholly free of him in their incarnate form, and their bodies had an effect upon their spirits. But in this way Morgoth lost (or exchanged, or transmuted) the greater part of his original “angelic” powers, of mind and spirit, while gaining a terrible grip upon the physical world. For this reason he had to be fought, mainly by physical force, and enormous material ruin was a probable consequence of any direct combat with him, victorious or otherwise.
—-
This is the chief explanation of the constant reluctance of the Valar to come into open battle against Morgoth. Manwë’s task and problem was much more difficult than Gandalf’s. Sauron’s, relatively smaller, power was concentrated; Morgoth’s vast power was disseminated. The whole of “Middle-earth” was Morgoth’s Ring, though temporarily his attention was mainly upon the North-west. Unless swiftly successful, War against him might well end in reducing all Middle-earth to chaos, possibly even all Arda.
—-
It is easy to say: “It was the task and function of the Elder King to govern Arda and make it possible for the Children of Eru to live in it unmolested.” But the dilemma of the Valar was this: Arda could only be liberated by a physical battle; but a probable result of such a battle was the irretrievable ruin of Arda. Moreover, the final eradication of Sauron (as a power directing evil) was achievable by the destruction of the Ring. No such eradication of Morgoth was possible, since this required the complete disintegration of the “matter” of Arda.
Morgoth’s Ring - The History of Middle-Earth - J.R.R. Tolkien