I am assuming that your question is meant to help you write a paper on "The Necklace." This is a story that has many themes, and to relate a topic back to your reader, you want a theme that the reader can relate to. Let's look at a few.
You could discuss the theme of greed in the story. That is something every reader can relate to. Sometimes we have been greedy ourselves or we know someone who is greedy. We like to think that people who are greedy will not do well, and in this story, that is a very clear message.
The theme of dishonesty is one that most readers are interested in. Madame Loisel's troubles really begin because she wants to present herself in a dishonest way, and she makes matters worse when she fails to tell her friend she has lost the necklace. Again, readers want to think that dishonesty is punished somehow, and the story does show this.
Another interesting idea to explore, one that most readers would probably find interesting, is that this story has some similarities to the story of Cinderella. Madame Loisell is a poor girl, like Cinderella, and she is invited to a ball. At the ball, she loses a necklace, rather than a shoe. At this point, of course, the story becomes different from Cinderella's story, since there is no prince to rescue her. But there are probably enough comparisons to make for a good paper that readers could relate to.
When you are looking for a topic that readers can relate to, what you want to focus on are the elements of the story that are universal, elements such as greed or envy, elements such as love or hate. Most readers have experienced these feelings, so they can identify with what you have to say about the story.