[Jacob:] My knees trembled; I struggled to hold myself upright while the voice of the Alpha lashed at my will. (10.252)
Jacob struggles with what he should obey, his werewolf instincts or his human instincts. So is loyalty to a leader important in war?
[Jacob:] That's why we would be able to kill him – because he wouldn't want us, his enemies, to die. (10.263)
Jacob believes that although Sam has decided to fight them, he'd rather die himself than kill his own brothers.
[Edward to Jacob:] "I think of you as a… a brother in many ways. A comrade in arms, at the very least." (17.123)
Edward means to say that, despite their differences, they've always fought on the same side together. They've always done their best to make Bella happy, and now they're both fighting for her to survive.
[Leah to Jacob:] "But he's your best friend, Jake. He and Quil would rather stand behind you than face you in a fight." (13.285)
Leah believes that Embry and Quil's friendship with Jacob is stronger than their loyalty to the pack and that they would even protect their enemies, the Cullens, just to be on Jacob's side.
[Carlisle to Jacob:] "Jacob, you can't fight against your brothers… I didn't mean that you would be… incapable. But that it would be very wrong. I can't have that on my conscience." (14.110)
Carlisle believes that it's wrong for Jacob to fight against his own kind. But he seems to be more concerned about his own conscience than Jacob's.
[Bella:] The main thing was the end of the feud with Sam's pack… because the most absolute of the pack laws was that no wolf ever kill the object of another wolf's imprinting…The pain of such a thing would be intolerable. (23.32)
Bella suggests that the pack has ended their feud and won't harm Renesmee because if they did, Jacob's pain would affect them all.
[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.
[Bella:] This was the ploy. [Caius] had not wanted Irina's complaint; he had wanted her defiance. His excuse to destroy her, to ignite the violence that filled the air like a thick, combustible mist. He had thrown a match. (37.66)
Bella realizes that Caius tried to start the war in a way that would pin the Cullens and their friends as the aggressors, and the Volturi as victims, forced to act in self-defense.