In Letter 142, Tolkien called the Lord of the Rings a "Catholic work", quote:
The Lord of the Rings is of course a fundamentally religious and Catholic work; unconsciously so at first, but consciously in the revision. That is why I have not put in, or have cut out, practically all references to anything like 'religion', to cults or practices, in the imaginary world. For the religious element is absorbed into the story and the symbolism. However that is very clumsily put, and sounds more self-important than I feel. For as a matter of fact, I have consciously planned very little; and should chiefly be grateful for having been brought up (since I was eight) in a Faith that has nourished me and taught me all the little that I know; and that I owe to my mother, who clung to her conversion and died young, largely through the hardships of poverty resulting from it.
Of course, some parallels with Christianity are obvious, like Gandalf's resurrection. But what makes this book closer to Catholicism in contrast to other branches of Christianity? Did Tolkien ever elaborate on this? Or did he ever mentioned what in Catholicism made him personally prefer it over, say, Anglicanism, except of it being the faith of his parents?