How we cite our quotes:
[Bella:] They came with pageantry, with a kind of beauty. They came in a rigid formal formation. They moved together, but it was not a march; they flowed in perfect synchronicity… (36.1-2)
Bella describes the Volturi's advance as "beautiful" because, despite their enormous numbers, they appear as one, powerful unit. If they'd arrived as a wild horde of bloodthirsty vampires, would they have appeared more frightening or powerful?
[Bella:] I heard the beating of large hearts, closer than before. I risked glances to the left and the right… to see what had stopped the Volturi advance. The wolves had joined us. (36.24)
Obviously the appearance of the wolves compromises the Volturi's confidence, because it introduces an element of surprise in their well-rehearsed battle plan.
[Bella:] And we were going to lose. Abruptly, I was furious. Beyond furious, I was murderously enraged. My hopeless despair vanished entirely… all I wanted in this moment was a chance to sink my teeth into them… I could have danced around the pyre where they roasted alive. (36.28)
When Bella realizes that everyone she loves will die, including her, the injustice of the situation fills her with so much rage that her feeling of powerlessness morphs into a death-defying urge to fight.