In Stopping by Woods on a Snowy Evening by Robert Frost what does the word sleep symbolize?

In the line about "and miles to go before I sleep," the Word refers not just to going to bed at the end of a long day, but it also symbolizes a person's death. The poet knows he could remain in the woods and marvel at nature's beauty and the falling snow, but he has "promises to keep" and he knows his life is not over yet; he has obligations he must fulfill (perhaps to God?) before his time comes.