What is the moral lesson of a rose for Emily?

There could be more than one answer to this question. One answer would be a warning against pride. The Griersons' held themselves to the highest standards and this resulted in Emily's father being overprotective and chasing off all of her suitors. In the end, her father died and she became desperate to find someone. Once she found Homer, she was not able to let him go and would go as far as to kill to keep him with her.