I felt that [the thought] was of joy—of hope; but I felt also that it had perished in its formation. In vain I struggled to realize—to regain it. Long suffering had nearly annihilated all my ordinary powers of mind. I was an imbecile—an idiot.
This quotation appears as the narrator lies bound by straps, watching the pendulum above him. After eating some of the meat provided to him, he almost comes up with a plan for escape, but can’t quite complete the thought, leaving him in despair. Without this hope for escape, the narrator feels powerless. Not long after this moment, the narrator loses consciousness, as if to mimic the death that awaits him. Judging by his loss of consciousness and his reference to himself as “an imbecile—an idiot,” it seems that hopelessness saps the narrator of both his mental and physical faculties.
It was hope that prompted the nerve to quiver—the frame to shrink. It was hope—the hope that triumphs on the rack—that whispers to the death-condemned even in the dungeons of the Inquisition!
This quotation appears when the narrator no longer wants to succumb to the pendulum, and this hopeful momentum leads to him formulating his plan for escape. Hope here starts small, a quiver, and then grows, causing his body to shrink away from the blade. As he sits with this hope, however, it becomes powerful enough to imagine triumphing on the torture rack, a place with truly no escape. While losing hope, as he did previously, renders him an idiot, holding on to hope fires up his brain, leading him to devise an escape.