I like this interpretation:
From:
http://www.gradesaver.com/the-poetry-of-robert-frost/study-guide/section15/
The poem was inspired by a particularly difficult winter in New Hampshire when Frost was returning home after an unsuccessful trip at the market. Realizing that he did not have enough to buy Christmas presents for his children, Frost was overwhelmed with depression and stopped his horse at a bend in the road in order to cry. After a few minutes, the horse shook the bells on its harness, and Frost was cheered enough to continue home.
The narrator in the poem does not seem to suffer from the same financial and emotional burdens as Frost did, but there is still an overwhelming sense of the narrator’s unavoidable responsibilities. He would prefer to watch the snow falling in the woods, even with his horse’s impatience, but he has “promises to keep,” obligations that he cannot ignore even if he wants to. It is unclear what these specific obligations are, but Frost does suggest that the narrator is particularly attracted to the woods because there is “not a farmhouse near.” He is able to enjoy complete isolation.
Frost’s decision to repeat the final line could be read in several ways. On one hand, it reiterates the idea that the narrator has responsibilities that he is reluctant to fulfill. The repetition serves as a reminder, even a mantra, to the narrator, as if he would ultimately decide to stay in the woods unless he forces himself to remember his responsibilities. On the other hand, the repeated line could be a signal that the narrator is slowly falling asleep. Within this interpretation, the poem could end with the narrator’s death, perhaps as a result of hypothermia from staying in the frozen woods for too long.
The narrator’s “promises to keep” can also be seen as a reference to traditional American duties for a farmer in New England. In a time and a place where hard work is valued above all things, the act of watching snow fall in the woods may be viewed as a particularly trivial indulgence. Even the narrator is aware that his behavior is not appropriate: he projects his insecurities onto his horse by admitting that even a work animal would “think it queer.”
thanks