her as she wishes to appear at the fancy ball. Symbolizing innocence, purity, and conservativeness, the pearl necklace is too staid for Mathilde. Also, she certainly is not behaving innocently or honestly by wearing something that is not hers. Instead, she goes out of her way to borrow and show off something that is not actually hers in order to look like someone she is not: a wealthy woman.

Next, she tries on but is not satisfied with a “Venetian cross in gold and gems, of exquisite workmanship.” Mathilde surely is not behaving in a pious manner by coveting material riches. Instead of worshiping the religion of Christianity—as symbolized by the decorated cross—she reveres expensive objects and money. She cannot even appreciate the jewelry’s “exquisite workmanship” or high-quality craftsmanship. She pays attention to superficial appearances only.

At last, she spies “in a black satin case, a superb diamond necklace.” In contrast to the “large box,” the “black satin case” seems more ornate and sinister. The black color symbolizes darkness and evil. Her attraction to the shiny satin black box will result in dark days of stress and poverty. The word “case” suggests confinement, which is what she will experience during the next decade of paying off debt. The flashy and hyperbolically magnificent diamond necklace seems to cast a spell on Mathilde. As she fastens it “round her neck,” it becomes like a millstone or burden, symbolically foreshadowing the enormous debt that she will incur to replace it.

Early in this scene, Madame Forestier tells Mathilde to “Choose, my dear.” Mathilde’s choice of the diamond necklace ultimately leads to other fateful choices­—her decision to secretly replace the lost necklace with another one, her decision to work and pay off her debt (although that might not have seemed like much of a choice), and her final decision to admit the truth to Madame Forestier. The younger Mathilde acted helpless in her life as a resentful middle-class housewife aspiring for more, but the older Mathilde took control of her life, her choices, and ultimately her identity.

One could say that the black satin box in which Madame Forestier keeps the fake diamond necklace is deeply symbolic. It conjures up images of Pandora's box, an artifact in Ancient Greek mythology which, when opened, unleashed all manner of evil upon an unsuspecting world. Opening Pandora's box has come to mean doing something that will cause unforeseen problems, and that's definitely what happens in "The Necklace" when Mathilde opens up Madame Forestier's jewelry box.

As far as she's concerned, she's simply borrowing a beautiful diamond necklace that will make her the belle of the Education Ministry ball. But unbeknownst to her, she's about to land herself in a whole bunch of trouble, leading in due course to a lifetime of hard toil, poverty, and misery.

The mirror is a main symbol in this passage, symbolizing Madame Loisel's narcissism. She is in ecstasy looking at herself in an array beautiful jewels in the mirror. We learn that

She tried on the jewelry in the mirror, hesitated, could not bear to part with them, to give them back.

Part of the reason she asks if there are more jewels is that she doesn't want this sublime moment to end.

The black satin case—almost coffinlike—that the diamond necklace is in is also a symbol: the blackness is an ominous symbol of what the necklace will become for the Loisels. Yet once again, faced with a mirror reflecting back to her her ideal image as the wealthy, bejeweled woman she would like to be, Madame Loisel is mesmerized. This is her heaven:

She fastened it around her neck, over her high-necked dress, and stood lost in ecstasy as she looked at herself.

Her self-love seemingly has no end.

Finally, that a fake diamond, a gaudy piece of glass, what sets Madame Loisel's heart to "beat with uncontrolled desire" symbolizes how much she lives by appearances. She is unable to evaluate the true value of things.

In the story “The Necklace”, the lost necklace stands for lost hopes and dreams for Madame Loisel.  It also represents her greediness and her disingenuousness because she only judges herself by what she has, and it is her belief that others will do the same. The necklace with the  artificial diamonds represents the artificiality of her character. People admiring the necklace only for its supposed value have been deceived. Just because something looks real doesn’t mean that it is. Just because Madame Loisel looks upper-class at the ball doesn’t mean that she is.   The real necklace stands for honesty and originality, which are not represented by Madame Loisel at all, but do seem to come across in her poor beleaguered husband and her friend.

The meaning of the lost and real necklace are intertwined. When the Loisels first borrow the necklace, they think it is real, and, while they know they don't own it, they think that if it looks like she/they own it, their own value will be increased. Appearance will trump reality. Once they lose it, they have to buy a real replacement. They must work hard to pay for it, and in the process, Madame Loisel loses much of her original beauty, which was real.

The meaning of both is that if you confuse appearance with reality, you will suffer, and that making an illusion real (paying for a real replacement) would cost intense work.
Greg

It is interesting to consider Madame Loisel's choice of the necklace from all the other jewelry her friend Madame Forestier offered her. Mme. Loisel tried on some bracelets, a pearl necklace, and a Venetian cross in gold and gems--but when she saw the diamond necklace she knew that was exactly what she wanted.

Suddenly she discovered, in a black satin case, a superb diamond necklace; her heart begana to beat covetously.

The other jewelry Maupassant mentions is relatively modest, but the diamond necklace looks "superb." Her choice of this splendid necklace shows the magnitude of her dreams of glory. Maupassant does not describe it in any detail, but we can imagine it as quite large and covered with glittering diamonds. It is almost as if the necklace, which is featured in the story's title, symbolizes the life Mme. Loisel would like to have, with a home, splendid furniture, servaants, important friends, and gentlemen admirers.

The necklace can also represent a chain around her neck. Most women's jewelry can be seen as symbols of chains and shackles. It is also an item of such extreme apparent value that, once lost, it is unlikely ever to be recovered. Her husband goes out and spends hours retracing the path they took from the Ministry to their home.

And he went out. She remained in her evening clothes, lacking strength to get into bed, huddled on a chair, without volition or power of thought.

What chance has he of finding a big, ostentatious diamond necklace which has apparently slipped off and fallen on the ground? Nothing could be more conspicuous. The first passer-by will spot it. Whoever finds it will be overjoyed. It is an experience that happens once in a lifetime--if ever. It looks so valuable that the discoverer, however moral, would find it impossible to return it to its owner. A necklace like that, if real, could cost as much as a million dollars in today's American dollars. (Maupassant discusses actual prices of jewelry in another story, "The False Jewels.") That was why choosing it to wear to the ball was a fatal mistake.

The Necklace is a story that can be taken literally or symbolically—it works either way.

Sometimes students have difficulty with symbolism because it involves thinking figuratively. That means you have understand what an author is representing, rather than what the author is actually (literally) saying.

In this story, think about what the necklace causes in the lives of the Loisels. At first, it makes Mathilde feel beautiful. But later, when it is lost, they have to change their lives to pay for Madame Forestier's necklace. Finally, it turns out that the necklace was worth very little. If they had know that, they never would have had to sacrifice themselves to make the money to pay her back.

Now think about what in life affects people this way. In other words, what might make us feel beautiful, or important, but end up consuming our lives in a way that turns out to be wasteful and unnecessary?

The answer to that question should be the answer to your question, what does the necklace symbolize?

I would say that the necklace symbolizes the pursuit of wealth or fame. It makes us feel good for awhile, but it can become burden, eventually coming to dominate our lives in a way that makes us unhappy.

However, it is interesting to note that the writer, Guy de Maupassant, doesn’t leave things quite so simply tied up in a neat little package.

Look at how Mathilde felt in the beginning of the story:

Mathilde suffered ceaselessly, feeling herself born to enjoy all delicacies and all luxuries. She was distressed at the poverty of her dwelling, at the bareness of the walls, at the shabby chairs, the ugliness of the curtains.

It turns out, ironically, that all of the effort that Mathilde had to put into working to repay the cost of the necklace did not make her miserable. On the contrary, the fact that she had to pretty much give up her fantasies of the good life and focus on a life of hard work seems to have made her a little happier, or at least less discontented. This could symbolize the idea that a simple life of honest work is a happier way to live than wishing for things that you cannot have. Late the story, she has become an admirable character:

Thereafter Madame Loisel knew the horrible existence of the needy. She bore her part, however, with sudden heroism. That dreadful debt must be paid. She would pay it.

The borrowed necklace itself is a good symbol because of the fact that it looks beautiful and expensive but is made of false jewels. Mathilde is susceptible to being deceived and misled by meretricious things. She lives in a fantasy world. Losing the borrowed necklace makes her wake up to reality. Maupassant was a realist, like his uncle and mentor Gustav Flaubert. He was also strongly influenced by the German pessimistic philosopher Arthur Schopenhauer, who once wrote:

It is very important for us to learn early in youth that we are living in a masquerade, otherwise we shall be unable to grasp and get at many things but shall stand before them quite puzzled; and indeed those will stand longest who ex meliore luto finxit praecordia Titan. ('Whose heart was fashioned by Titan out of better clay,' Juvenal, Satires, XIII, 183). . . Almost invariably, the genuine article is rejected and the merely spurious sought. And so young men should be taught that in this masquerade the apples are of wax, the flowers of silk, the fish of cardboard, and that everything is a plaything and a jest. 

Part of Mathilde's great social triumph at the Minister of Public Instruction's ball is due to the fact that, like Cinderella in the fairy tale, she makes a great impression with a necklace that is not her own and a gown her husband could barely afford.

The fake necklace also symbolizes youth, grace, charm, and beauty. It is a useless luxury item appropriate to the wastefulness and privilege in the lives of shallow people. Sir Francis wrote in his essay "Of Riches":

Do you not see what feigned prices are set upon little stones and rarities? and what works of ostentation are undertaken, because there might seem to be some use of great riches?