Whose woods these are I think I know.
His house is in the village though;
He will not see me stopping here
To watch his woods fill up with snow.
My little horse must think it queer
To stop without a farmhouse near
Between the woods and frozen lake
The darkest evening of the year.
He gives his harness bells a shake
To ask if there is some mistake.
The only other sound's the sweep
Of easy wind and downy flake.
The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
The narrator, on the other hand, hears the horse but doesn’t end his contemplation just yet. The speaker returns to the practical description of the noise of the wind and snow.  The lyrical-sounding easy wind, the “downy flake” (downy means feathery), is evocative of relaxation and rest. The sublime woods sing a siren song to the narrator, drawing him in. The impulse could lead to enjoyable ends, or — if the death analogy is correct — it could be a deadly decision. 
 
 One can also note the onomatopoeic quality of this line, where the words mimic the sounds of the air: “sound’s the sweep,” “easy wind.”
Stopping by Woods on a Snowy Evening