The title points to Keats's nightingale, and the poem seems to answer that old image of a bird that outlasts us. Here the bird is a "she," and her song does something quieter than offer escape: it makes us "see our passing / is common as ash." Death is ordinary, not special, and the poem says so plainly.
The images are hard to pin down. "Mouth gone down / towards the owl" suggests a voice sinking toward night and silence. The "fine hands over the night" may be the singer's, or the bird's wings, and what they sing is "what we serve," which hints at a sense of duty or devotion we don't often name.
The ending turns warmer. "The stuff and flutter of living" is messy, small and alive, and the final line, "more than others," leaves open what exactly it is more than. The mood is hushed and accepting. The speaker seems to find a kind of dignity in being briefly, fluttering alive, even while facing ash.