How does the dual narrative help to arouse your sympathy for Victor and the creature in "Frankenstein"?
(You've heard Victor's side of the story for most of the book but know you also hear it from the creature's point of view)
The dual narrative is very effective because, first we get to know Victor's feelings very intimately. The reader understands how Victor is driven to create the monster, how he feels after the monster kills.
When the creature begins to narrate his humanity is revealed, he is sensitive, and almost innocent in his curiosity. You can't help but feel sorry for the creature, he did not ask to be born, he is alone, abandoned, lonely and can't help his responses to certain situations.
For me, hearing from the creature helps to create sympathy for both Victor and the creature. For Victor for his misguided use of science and for the result of his efforts, the creature.
Well, to be honest, as a personal note, I'm not sure it does: the layered narrative—more than doubled—sometimes feels like it distances me from the action, and makes me feel less (and think more). However, when the dual narrative does work to arouse sympathy, it is for several reasons. First and most simply, it fills in gaps in the story. Closely related, we get to know the creature as a being, not just an object. Second, we get the creature's side of the story too. That means he isn't just a shameful mistake. He's a feeling, thinking person. Third, we see how much pain each has suffered, and fourth, we see how bound up they are.