A speaker burns their own old manuscript, and the poem watches it go. The opening metaphor does most of the work: fire becomes a "thorough & voracious reader," one that takes in every page, one after another, until nothing is left. It's a strange compliment. The fire pays the writing more complete attention than any human audience might have, yet that attention destroys it.
The speaker doesn't sound angry or panicked. The details are quiet: pages turning "gray & brittle," then rain and mist settling over the smoking pile. The final image, a "long thin sigh," could be the smoke itself, or it could be the speaker's own breath, or the sound of the work giving up. The poem doesn't say which, and that ambiguity is part of its pull. The mood is calm, wistful, and a little resigned, as though letting go of old writing brings both relief and loss.