How does the first paragraph help develop the plot?

Mathilde is born to a low-class family; with no money for a dowry, she is married to Monsieur Loisel, a clerk from the Board of Education. Mathilde–now Madame Loisel–had always felt like she should have been upper class, and is unhappy in her married life: she hates their home, their food, and her lack of fine clothing and jewelry. One evening, her husband excitedly presents her with an invitation to attend an event at the Minister of Public Instruction’s home. To the surprise of M. Loisel, Mme. Loisel throws the invitation down in dismay, weeping and complaining that she has nothing to wear to such an event. Her husband offers to give her the money for something suitable, but as the day of the ball approaches, she is still dismayed. When asked why, she replies that she is embarrassed to attend the ball without any jewels. Her husband suggests that she ask to borrow some jewels from her rich friend, Madame Forestier. She agrees and goes to see her friend the next day, greedily choosing one of Madame Forestier’s finest necklaces.