Whose woods these are I think I know. A
His house is in the village, though; A
He will not see me stopping here B
To watch his woods fill up with snow. A
My little horse must think it queer B
To stop without a farmhouse near B
Between the woods and frozen lake C
The darkest evening of the year. B
He gives his harness bells a shake C
To ask if there is some mistake. C
The only other sound's the sweep D
Of easy wind and downy flake. C
The woods are lovely, dark and deep, D
But I have promises to keep, D
And miles to go before I sleep, D
And miles to go before I sleep. D
The rhyme scheme in the first stanza is AABA. In the next stanza the poet picks up the B ("here") and the rhyme scheme for that stanza is BBCB. Then he picks up the C ("lake") and the rhyme scheme for the third stanza is CCDC. And the final stanza picks up the D ("sweep"). The final stanza is straight DDDD. The effect of this rhyme scheme seems to be to mimic the impression of gently falling snowflakes, and the final stanza seems to be intended to suggest the buildup of snow on the ground.
Of course, there is a great deal more to the poem than the impression of falling snowflakes, but the speaker does say that his purpose in stopping by these woods on a showing evening is to "watch his woods fill up with snow." So the reader may have the illusion of watching the falling snowflakes along with the speaker which is enhanced by the rhyme scheme. There is a definite falling effect in the AABA, BBCB, CCDC, and then an impression of deepening snow at the "bottom" of the poem. The snow is not falling heavily. The speaker describes the weather conditions as "easy wind and downy flake." The flakes are floating down slowly, and the rhyme scheme seems to suggest that familiar sight. The B in the first stanza might be considered a drifting snowflake which lingers throughout the second stanza, and so on. If the snow were falling heavily, the speaker probably would not have stopped there that night.
The repetition of the words "And miles to go before I sleep" with the two D rhymes at the very end has suggested to some readers that the speaker is having sombre thoughts and might even be thinking of walking out into the beckoning woods and letting himself freeze to death. Frost repeatedly denied this. The thought that he has miles to go before he sleeps could also be interpreted to mean that he expects to have a long life ahead of him with many things he wishes to accomplish--which in fact was the case. He wrote the poem in 1922 and died in 1963. He was nearly eighty-nine years old.