Winter's end is usually pictured as a loss, and the title, "The death of winter," seems to promise that. The poem begins that way too. On a warm day, a patch of ice goes dull "like a dead eye," a bleak and slightly unsettling image of something losing its sight and its hardness.
Then comes the turn. Something moves under and through the ice, and the speaker compares it to the soul, "that bubble of breath." A trapped air bubble drifting in melting ice becomes a small sign of life, fragile but real. It sits surrounded by meltwater and a bluebird's song, so the ending opens out into sound and movement.
The speaker seems quietly fascinated rather than sad. The mood is gentle and hopeful, with a hint of mortality still in it. Winter dies, but its death lets something else begin, and the poem suggests the soul might be just as light and just as lasting.