There are of course a number of different examples that you could cite. My own favourite comes at the very end of the story, in the Epilogue, when the narrator considers the import of the Time Traveller's story and what the truth of it would mean to humanity. Having narrated quite a hopeless tale of the fate of humans, and how the quest to make life easy and comfortable has ironically lowered the human spirit, the narrator now contemplates the future in quite a hopeless fashion. Note the metaphor that he uses to describe the future:
But to me the future is still black and blank--is a vast ignorance, lit at a few casual places by the memory of his story. And I have by me, for my comfort, two strange white flowers--shriveled now, and brown and flat and brittle--to witness that even when mind and strength have gone, gratitude and a mutual tenderness still lived on in the heart of man.
The future, then, to the narrator is "a vast ignorance," with only the memory of the Time Traveller's tale to give it occasional light. Interestingly, the two flowers that Weena gave the Time Traveller are used as symbols of hope and how, no matter how much man changes, there will always be some element of gratitude and tenderness in him.