Two short images carry this tiny poem. In the first, evening "burrows into the sand," as if darkness were a small animal digging itself a hiding place at the edge of a beach. The light fades, and night settles downward into the ground rather than falling from above.
The second image turns to the speaker. They have "less heaven than my eyes," which is a puzzling, lovely line. One way to read it is that the eyes can take in a vast sky, but the speaker's own life, spirit, or hope doesn't match what they see. The sky is big, and the person looking at it feels small and tied to the earth, which fits the title, "Earth-bound."
The mood is quiet and a little wistful. The speaker isn't angry or desperate, just aware of a gap between what they can see and what they can reach. The poem leaves that feeling open, like the dimming light.