This passage from the Ainulindale captures well Tolkien’s ability to bring together and harmonize two otherwise very distinct literary and emotional themes:
Never since have the Ainur made any music like to this music, though it has been said that a greater still shall be made before Iluvatar by the choirs of the Ainur and the Children of Iluvatar after the end of days.
On the one hand, in the unrepeatability of the original Music of the Ainur, we have the idea of a longed-for yet lost and irretrievable past that dominates much of Tolkien’s writing. On the other hand, in the very same sentence, Tolkien balances this nostalgic theme with the uniquely Christian hope and expectation that, within time, we will also see all things made new, every hurt mended, and every desire fulfilled. Call this Tolkien’s “romantic eschatology.”