Snow is the subject here, though the word never appears. The speaker calls the flakes "feathers" and keeps coming up with new pictures for them: rivers flowing off to distant places, stars that have tumbled out of the dark, tiny cities, even something shed by singing angels. The opening stanza returns at the end almost unchanged, so the poem feels like a loop, much like snow that keeps falling.
The speaker seems awed and gently affectionate. Snow is beautiful and light, but it also brings a hint of danger, as the "sharp shards" and the way it "envelops entire lands" suggest. Still, the softer feeling wins out. The line about "making small hearts soften" suggests that the snow calms even small creatures. The mood is quiet, hushed and dreamlike, with a sense of wonder at something that seems to come straight from the heavens.