The first stanza of the poem is rather simple and provides the basis for the imagery. It mentions the woods and implies that they are located away from town and civilization "his house is in the village though". It also shows the easy pace that speaker is taking, having plenty of time to simply watch the falling snow. As I think about them, the words of the first stanza are not overtly somber, they do however through their order and the way they were chosen create a rather pensive mood.
The second stanza provides a more in depth view of the imagery sketched out in the first; it also provides a more definite time and location. The first two lines of this stanza firmly place the reader rather deep in the woods and away from any dwelling. He is so far out in fact that his horse is puzzled by his actions. The next line gives a better image of the scene "Between the woods and frozen lake"; it seems to be a rather quiet and lonely place. The next line then provides that it is night and very dark, either emotionally or actually. I think that Frost intended to make that line rather ambiguous "The darkest evening of the year", It can either be taken literally as the most lightless night, or it can be taken as the night of the darkest emotions. I think that it is a combination of the two, a dark moonless winter night in which the speaker experiences some form of depression or loneliness. The third stanza of the poem brings the strangeness of the situation to a head.

The only other living being in this cold lonely landscape, the speaker's horse takes action to find the reason for the odd stopping. The noise from the inquisitive harness bells provide contrast to the quiet of the scene, where the only other sounds a wind and snow. The descriptions of the sounds provide a little insight to the speaker's mindset and position. He is so still that he can here the soft fall of the "downy flake" and hear the movement of the "easy wind". This also shows a great calm and patience that the speaker must posses. The final stanza of the poem brings all the sentiments of the poem together, an intense love and awe of nature, a never ending patience and some unknown task or problem that robs the speaker of rest. The "dark and deep" woods seem to reflect the speaker, his dark emotion and depth of character. There stillness also contrasts with the need of the repeated closing lines "And miles to go before I sleep/ And miles to go before I sleep". These final lines represent the problem that has plagued the speaker and that is most likely responsible for his dark mood. It is something that is undefined that does not demand a rush to deal with, but is important enough to demand attention.