The narrator is telling the story partly as he learns it and partly as he reflects on it. He also uses the variation in chronological order to keep us wondering what Miss Emily might be up to (she is a mysterious figure) so there can be foreshadowing. Further, the change in chronological order helps us to focus on the ante-bellum South and its attitudes which have made Miss Emily feel she should be treated in a certain way. This belief that she has is contrasted by the behavior of the newer generation.