There are contexts, obviously, when it is perfectly sensible to ask what a poem means. For a student reading Frost's "Stopping by Woods on a Snowy Evening," it is quite reasonable to ask what Frost means by looking into the lovely, dark woods and then saying "But I have promises to keep / And miles to go before I sleep." It is also fairly easy to answer: he means that oblivion is tempting, but there are reponsibilities the living must honor. It is less easy to answer the question "What does the repetition of the phrase 'miles to go before I sleep' mean?" In fact, it may be a meaningless question. More on this later.