Because if you're going to painstakingly create a new language from scratch, you damn well are going to use it. The poem is Namárië .
The First Stanza Of Namárië In Elvish
The First Stanza In English:
Ah! Like gold fall the leaves in the wind,
Long years numberless as the wings of trees!
The long years have passed like swift draughts
Of the sweet mead in lofty halls
Beyond the West, beneath the blue vaults of Varda
Wherein the stars tremble
In the voice of her song, holy and queenly
You can read the whole translation here.