The idea of book-burning is one usually associated with censorship and acts contravening freedom of speech, a practice most closely associated with the Nazis, who burned anything they felt was ideologically impure. This poem is interesting in that its viewpoint is quite different from what the title might suggest. Some books, the speaker states directly, "deserve to burn." What is up for discussion is how far we ought to feel sympathy for the speaker's provocative viewpoint.
In the first stanza, the speaker describes the image of a book being burned and mentions that truth can be "brittle" and easily destroyed—preserved for a time while the fire rages but ultimately consumed. This is a troubling image and runs contrary to the more frequently cited statement that one cannot destroy an idea.
The second stanza, however, sheds some light on the speaker's meaning. His concern here is that many books have been written that do not deserve to be written—again, an issue worthy of debate. But what the speaker highlights is that so much has gone unwritten, and this has allowed ignorance to grow unchecked—when a book is burned, it draws attention to the truth it contained, whether or not that truth is ultimately defeated.
This is a difficult and thought-provoking poem about censorship, truth, and the worthiness of ideas.