One theme that pervades Faulkner's work is the conflict between the "Old South," pre-Civil War southern society, and the "New South," the post Civil War and Reconstruction south. In "A Rose for Emily," he explores how the Old South, represented by Miss Emily, interacts with the New South, represented by the town of Jefferson, which functions as a character in the story.
In most instances, Miss Emily, representing what is left of the aristocracy of the pre-Civil War south, manages to overcome the democratic, class-leveling New South. For example, when members of the Jefferson town council visit Miss Emily and attempt to get her to pay taxes, she relies on the fact that, years prior, Colonel Sartoris, a leader of the town and part of the Old South, remitted her taxes permanently because her father had loaned the town some funds at some point. Emily's response to the demand that she pay taxes is, "See Colonel Sartoris. I have no taxes in Jefferson," and the town council members were beaten in this encounter, "horse and foot."
Later, when the town is scandalized by Miss Emily's affair with Homer Barron, a man who works with his hands and, worse, a Yankee, the town calls in Miss Emily's cousins from Alabama to try to convince her to act like a proper southern aristocratic lady. As we know, they fail in this attempt as well.
Faulkner disclosed his real motivation for writing this story, however, in a 1959 interview in which he said that he wanted to tell a story of a blighted life--the tragic life of someone who had normal aspirations for a life with a husband, a home, children, and then was "brow-beaten and kept down by her father," who selfishly only wanted a house keeper and consequently rejected every potential suitor as not suitable for Emily. Faulkner said that when someone's normal aspirations are crushed so brutally those aspirations might become twisted and become something very unnatural and tragic. Although Faulkner acknowledged Emily's moral and ethical failure, he ultimately felt that Emily was an object of pity rather than condemnation.
In essence, then, "A Rose for Emily" allowed Faulkner to pursue one of his favorite themes--the evolution of the Old South to the New South--and to examine the effects of psychological deprivation and cruelty.