Ever been curled up in bed at night when there was a storm outside? Maybe it wasn't a hurricane that felt like it was going to blow the house down – just a blustery, windy, rainy night. Remember the rain pattering on the roof? The wind swirling and howling outside? Those are the sounds we hear in this poem.
First, listen to the rhythm in the opening line: "The day is done and the darkness." There's a steady beat in there, but it isn't regular like a drumbeat. It doesn't go "da DUM da DUM da DUM." Here it's more like "da DUM da DUM da da DUM." Hear the difference? Read a few lines, and listen to how the beat jumps around a little without ever going away. We think that sounds like the drumming of the rain on the roof. Sometimes fast, sometimes slow, but steady and rhythmic all the time.
Now listen to the soft sound of the words: For example: "As a feather is wafted downward" (line 3). We hear the whooshing of the night wind in these lines – not sharp, crackling harsh sounds, but quiet, powerful, whispering words that seem to wrap themselves around you. We think Longfellow wants you to feel surrounded, almost cradled by these sounds, the way you would be by the sounds of the night. Then, just as you are drifting off to sleep, you hear the storm die out and "silently steal away" (line 44). That last line does a great job of both describing and sounding like a quiet ending, a return to peace and silence.