have often thought this poem deals with death. The poet stops and takes in the peaceful beauty and serenity of the snowy woods. He considers his options as the horse arouses him from his reverie. As is so often the case in Frost's poetry, a decision must be made. His choice here is to return to his life of promises, obligations that must be fulfilled before he can sleep.
This is a personal interpretation. That is the true beauty of great poetry, though. One can experience many things that are his alone.