In "Stopping by Woods on a Snowy Evening," by Robert Frost, the speaker of the poem (which of course is not necessarily Frost himself) stops his horse-drawn carriage (or sled, since it is snowing) in front of a forest (woods).
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.
As the last line of the stanza suggests, he simply wants to watch the snow falling on the trees. The second stanza, however, suggests something beyond an idyllic postcard-like winter scene. There is nothing nearby (note the sense of isolation) except a frozen lake, and it is "the darkest evening of the year."
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.
The third stanza reinforces the tranquility of this quiet winter scene by giving us the sound of harness bells and a gentle wind blowing the snow. The final stanza adds to the more ominous aspects of this peaceful scene.
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.
While the woods are lovely, they are also "dark and deep." The next word is but, implying that the speaker is somehow attracted to the deepness and darkness of the woods. It is perhaps a figurative longing for something more or even something darker and more sinister than his present life affords. Whatever longing he expresses, fulfilling it is not possible for him, as he has "miles to go" before he can stop to rest. Because the line is repeated, we get the sense that the speaker is weary of the path he is on and knows he cannot do the figurative exploring he longs to do.
What seems to be a simple stop to watch the snow is really a picture of the speaker's desire or attraction for something more and his regret that he can do nothing to satisfy it.