The main argument in "A Rose for Emily" is that the human condition is in constant need and search for some form of happiness. Unfortunately the ways in which we attempt to find it is what makes us less than perfect as a human race.
Since the human condition, among several definitions, is also described as
Man's strives to give order and meaning to his life, to reduce the mystery and unpredictability that constantly threaten him. (Abcarian and Klotz, 2006 in The Human Experience in Text)
then William Faulkner uses Emily Grierson's unfortunate circumstances to point out how this search for meaning and happiness can lead some individuals to consider chaotic measures.
All is explained to the reader by the townsfolk, who silently witness Emily's life from when she was young until the day of her funeral. They mention how Emily's father was so possessive of her and so selective for her that she rendered her incapable of becoming independent. The day of his death, Emily even refused to give up the body, or accept his death altogether.
The townsfolk realize then and there that Emily's restrictive upbringing, overprotective environment, and unrealistic view of the world (they were old South upperclass) are the very factors that will eventually bring her down.
So when she got to be thirty and was still single, we were not pleased exactly, but vindicated; even with insanity in the family she wouldn't have turned down all of her chances if they had really materialized.
After the father dies, Homer Barron is said to have had deserted her within a short period of time. Now we find Emily alone and feeling abandoned; she is also old, and with the same views of life as she had when she was young; her defenses are emptying, her needs have not been met at all, and typical of her human condition, Emily hopes for happiness.
Faulkner then observes how her desperation calls for extreme ideas; to lure Homer back, to kill him, and to keep his body with her forever. He even tells us how natural this seemed to her; how she prepared to lure him back, and how she created in her mind a scenario of marital bliss so exact that she replicated it in her house.
...we were sure that they were to be married. We learned that Miss Emily had been to the jeweler's and ordered a man's toilet set in silver, with the letters H. B. on each piece..she had bought a complete outfit of men's clothing, including a nightshirt, and we said, "They are married." We were really glad.
In the end, when the reader finds out about Emily's keeping of Homer's body is when all comes together and the case for the human condition is more illustrated: poor Emily Grierson lived an entire life being guarded from herself and the world around her; she never summoned her own abilities to give herself the wants and maybe even compensate for some of the needs that she obviously was so hungry for. The human condition dictates that when needs are not met, pathological behavior will occur as a result of the overcompensation of what we think are real needs. This is exactly what happened to Emily, as cleverly narrated by Faulkner.