why does the author have dana go back and forth in time as opposed to just being thrust back to the plantation for the duration of the book?

Ill she not be here anon? is she not hurrying to upbraid me for my haste? have i not heard her footstep on the stair? do i not distinguish that heavy and horrible beating of her heart? what is the effect of parallelism in this excerpt? it emphasizes usher’s misunderstanding. it emphasizes usher’s love for his sister. it emphasizes usher’s psychological fixation. it emphasizes usher’s melancholy nature.