How does Maupassant use irony to support plot and theme in the short story "The Necklace"?

The lovely Madame Mathilde Loisel "suffers incessantly"
because she does not own expensive jewels. When her husband brings home an invitation to
a ball, she becomes depressed even more so. She has nothing to wear to make her look
beautiful.

Then, Madame Loisel remembers her friend Madame
Forestier who owns jewels. Madame Loisel borrows what she believes to be an expensive
necklace. She is radiant at the ball. She has a magnificent evening. All the gentlemen
believe her to be the most beautiful woman there.

The irony
in this short story is that Madame Loisel believes she is wearing an expensive necklace.
In reality, the necklace is an imitation. It is a fake. Not knowing this, Madame Loisel
feels she is elegant in her false necklace.

If only Madame
Loisel had known that her beauty was exquisite because of her natural features, she
could have saved herself ten years of hard work. As it turns out, she loses the borrowed
necklace and works ten long years trying to pay off a debt she borrowed to replace the
necklace.

Ironically, Madame Loisel works ten long years to
pay for a genuine replacement necklace when the borrowed necklace was not real. The
irony is in the fact that she wore an imitation necklace that made her feel pretty. The
imitation necklace served its purpose although it did not cost a
fortune.

When Madame Loisel learns that the borrowed
necklace she lost was not real, she has already learned her lesson in humility. Her
appearance is haggard from ten long years of domestic work. Yes, she has worked ten long
years scrubbing floors to pay off the thirty-six thousand francs she borrowed to replace
the lost necklace.

The irony is that Madame Loisel looked
to be worth a fortune with the imitation necklace. Had she been contented with her
natural beauty, she could have saved herself years of toil to pay for a genuine
replacement necklace that substituted an imitation. Ironically, Madame Loisel learns a
lesson on humility from a necklace that was not even
real:

The
story's greatest irony, however, is embodied in the necklace itself; while it appears to
be a piece of jewelry of great value, it is really an imitation. The Loisels sacrifice
their humble but sufficient home to buy an expensive replacement for a cheap
original.