"Thanatopsis" is definitely a poem about death, but it’s also a nature poem. Human beings come and go, but nature is always there. The hills and rivers are eternal, huge, and almost intimidating. This isn’t Finding Nemo-style nature here. No cute little fishies. Just vast, powerful forces that swallow us up and keep right on moving. Nature isn't all cold and indifferent, though. The poem starts out with the idea that nature is like a nurturing, caring woman who comforts us when we start to fear death.
The natural images in this poem are largely free of particular details. This helps to maintain the poem’s overall focus on large ideas by avoiding distracting specifics.
The natural world is the ultimate source of comfort in this poem, taking away our pain by allowing us to see a world outside of our own misery.