Grondy beat me to the punch on the quote that ends Quenta Silmarillion. So many memorable quotes others cited do I love, but --out of memory error--. The one from Tolkiens letter about the significance of Frodos pity to his fate is very telling, and I've always loved Gandalfs words to him on the subject (hmm, connection?) So I'll go with my (other) most faves, and if they're all from the same source, well, that tells you something about me.
'Even now a Silmaril is in my hand.'
'Great is the Fall of Gondolin.'
And a final one I consider a quite profound and insightful, from the Ainulindalë.
The one was deep and wide and beautiful, but slow and blended with an immeasurable sorrow, from which its beauty chiefly came. The other had now achieved a unity of its own; but it was loud, and vain, and endlessly repeated; and it had little harmony, but rather a clamorous unison as of many trumpets braying upon a fwe notes. And it essayed to drown the other music by the violence of its voice, but it seemed that it/s most triumphant notes were taken by the other and woven into its own solemn pattern....
Then Ilùvatar spoke, and he said: 'Mighty are the Ainur, and mightiest among them is Melkor; but that he may know, and all the Ainur, that I am Ilùvatar, those things that ye have sung, I will show them forth, that ye may see what ye have done. And thou, Melkor, shalt see that no theme may be played that hath not its uttermost source in me, nor can any alter the music in my despite. For he that attempteth this shall prove but mine instrument in the devising of things more wonderful, which he himself hath not imagined.
Marred? Yes. Destroyed? No!
Edit: "inciteful" was perhaps a Freudian slip. The internet creates homophones, sorry.