There are small and large metaphors in “The Necklace.”
When Madame Loisel goes to the ball, she is “quite above herself with happiness.” (She isn’t literally over herself. She enjoys herself so much that she is “drunk with pleasure.”)
After the necklace is lost, her husband looks at the “agonising face of the future,” a vivid image, but definitely a metaphor, since the future has no face.
There are other small metaphors that are figures of speech—part metaphor, part tradition, like speaking of the “whole tribe of money-lenders,” which refers to the Jewish moneylenders.
The larger metaphor in this classic story, though, is the necklace itself. It is also a symbol for the realities of value, and how what you think matters often doesn’t, and how you often don’t value the things that matter most.
One large metaphor from the story is the invitation that Monsieur Loisel brings home to his wife. It is literally a ticket into a party where all the "really big people" will be, but it is metaphorically a ticket into 10 years of hard labor and degradation.
Madame Loisel felt trapped in the wrong life; she dreamed of having all the finer things she deserved because of her fine looks, grace, and charm. But, alas, she lived a modest life as the wife of a clerk in an apartment with one maid. Upon learning of the invitation to a party hosted by the Minister of Education and his wife, Madame Loisel insists upon procuring proper attire to wear amongst such fine people; this includes wearing real jewelry. After borrowing one of Mme. Forestier's diamond necklaces, she is excited to attend the party and mingle amongst the people whose class she so desperately wishes to be a part of. The night of the party, though, ends disastrously. Mme. Loisel has misplaced the necklace; she makes an exhaustive search for it, but is unable to find it. Her husband and she must replace the necklace, which requires her using her entire inheritance, borrowing from friends and crooks, and going into horrible debt. She and her husband dismissed their maid and moved into a smaller apartment.
They had to adjust to a life of "abject poverty." Her days filled with menial duties of cleaning, cooking, and going to the market. After meeting Mme. Forestier 10 years into this new life of always going without, the truth is unveiled: the necklace had been a fake.
The invitation to the party, then, welcomed Mme. Loisel (and her husband) into a hell of an existence.