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,
And miles to go before I sleep.
This line marks a major change in the narrator. He does not allow himself to enter the darkness of the woods.  The narrator is pulled back by his responsibilities and societal obligations, though the sublime beauty of nature and of death were enough to make him halt his journey for a while.
Stopping by Woods on a Snowy Evening