All our debate is voiceless here, As all our rage, the rage of stone; If hope is hopeless, then fearless fear, And history is thus undone.
What is the nature of their silence, their voicelessness? The speaker goes on to say that they're unable to give voice to their debate (or arguments). Nor can they rage. Their rage is "of stone." When's the last time you had an argument with a rock? We bet it didn't go well. That's the idea: what's human is silenced here.
Here come some more "-less" words: hope becomes hopeless, fear by logical extension (and parallelism) becomes fearless.
Sure, if you have nothing to hope for, then you probably shouldn't be fearing anything either (it's like the worst's already happened).
Still, we think that this lack is more related to the voicelessness of our lovers, the lack of a human element in the scene now.
Without these emotions, without the force of human response, history is "undone." Here nature is its own force. It turns rage into a stone. Compared to nature, human experience is drowned, and along with it any notion of human deeds or historical progress.
Man—that's quite a statement. See? We told you things were going to get darker.
On the bright side, our regular rhyming is back. (Check out "Form and Meter" for more.)