"The Bells" is not an obvious nature poem. It isn't about snowy woods, daffodils /wandered-lonely-cloud-daffodils/, or a nightingale. When you look again, though, you'll see that the poem is full of images from nature. Take, for example, the night, which is almost like a character in this poem, popping up in each section. Natural images like that help to structure this poem and tie it together, even if they aren't the main focus.
The poem is focused on the feeling and the experience of sound. Because of this, neither humans nor aspects of the natural world are given central roles.
As the poem changes, the meaning of the natural world changes. Things like the moon and the night, which had been comforting before, become dark and sinister