This paper analyses Tolkien's theological theory of evil: first its cosmological aspect (especially the relation between Eru and Melkor), then the place of evil in the structure of the world, the question of salvation, and finally, the question of the End and the second "Doom of Mandos" announcing Morgoth's fall.
Olszański, Tadeusz Andrzej
"Evil and the Evil One in Tolkien's Theology,"
Mythlore: A Journal of J.R.R. Tolkien, C.S. Lewis, Charles Williams, and Mythopoeic Literature: Vol. 21
, Article 44.
Available at: https://dc.swosu.edu/mythlore/vol21/iss2/44