In this poem, Stafford begins by condemning book burning, calling it "as hot as the fire lies make." He maintains that you can't entirely stamp out the truth by burning books, because a "few charred words" usually remain. To make this kind of claim about violent censorship or suppression of truth is fairly commonplace, but then Stafford makes a sharp turn.
In the second stanza, Stafford asserts there are other ways to suppress truth: you can write a book that tells lies and deserves to be burned, or more importantly, you can fail to speak at all. When you don't write the truth, you leave your society empty and savage:
More disturbing than book ashes are whole libraries that no one got around to writing----desolate towns, miles of unthought in cities, and the terrorized countryside where wild dogs own anything that moves.
Finally, in the very short stanza three, Stafford points to himself and calls himself a book burner because of all he's left unwritten and unsaid.
In other words, Stafford is calling on us to examine ourselves. It is very easy to point a finger and condemn those like the Nazis who burned books openly, but what is it that each of us does, or more precisely fails to do, that becomes a metaphoric book burning? What more can each of us do, Stafford asks, to bring truth to the world?
Poetry is challenging, that's for sure. However, figurative language may not be as mysterious as it sometimes seems. When working with figurative language, start first with the literal meaning, and then let yourself visualize what the poet describes. After that, let images and associations spill out, and you'll go a long ways.
In this case, the entire first stanza is an image of a book burning. There's not much theme there, just a shocking image of this burning. Book burning is associated with censorship: it is the most extreme form of censorship. Let that image stand for a while, then look at how the second stanza starts: "And some books ought to burn..."
A poet saying some books deserve to burn? That's another shocker. From that moment, the poem turns to its real purpose, which is talking about how not writing a book is a kind of censorship. Burning a book (the title) is unthinking it, letting your idea fall to ash, or go unlit.