Lily reminisces about her debut in society and how it was clouded by financial troubles. During this flashback, Wharton uses a metaphor of stormy weather to describe the effect of financial insecurity on Lily's youth, ultimately foreshadowing her troubles to come:
Lily was nineteen when circumstances caused her to revise her view of the universe. The previous year she had made a dazzling debut fringed by a heavy thunder-cloud of bills. The light of the debut still lingered on the horizon, but the cloud had thickened; and suddenly it broke. The suddenness added to the horror; and there were still times when Lily relived with painful vividness every detail of the day on which the blow fell.
This flashback to Lily's debut gives context to her present circumstances and attitudes towards money. A glimpse into her past like this helps the reader understand the transactional relationship between her youth and beauty and the ugly reality—having to marry for money—she now faces.
The metaphor of bills and debts mounting as being a “thundercloud”—and her successful debut as a “light” parting it—captures the duality of Lily’s situation even at this early age. Even her earliest introduction to society was somewhat overshadowed by her family’s lack of money. Their impending financial troubles literally cast a shadow over her youthful “light.” It's implied that she only made a successful debut because of her beauty: her financial troubles remain.
The mention of the stormy weather of her parents’ finances foreshadows the many money problems that will continue to plague Lily throughout the novel. The “blow” that Wharton refers to here is the news that Lily’s father is financially “ruined,” an event that starts a domino effect of cascading debt and failure. This sets up an expectation for the reader that Lily's journey will be fraught with challenges—an expectation that quickly proves to be true.
In a flashback, Lily recalls her mother's extravagant spending habits and her parents’ fraught marriage. In this passage, Wharton foreshadows similar financial and moral issues in Lily’s own future:
Mrs. Bart's worst reproach to her husband was to ask him if he expected her to 'live like a pig'; and his replying in the negative was always regarded as a justification for cabling to Paris for an extra dress or two, and telephoning to the jeweler that he might, after all, send home the turquoise bracelet which Mrs. Bart had looked at that morning.
This flashback to Lily's childhood shows her mother’s extravagant spending and her father’s passive, unhappy acceptance. This provides insight into the values and environment that shaped Lily's own views. The context of her upbringing gives the reader some background for Lily's obsession with social standing. It also gives the reader context for her (occasionally) snobbish view of others and her irresponsible attitude toward money. This passage is a not-so-subtle jab at the shallow and materialistic culture Lily and her mother are part of.
The conflict and underhandedness between Lily’s parents and her mother's “justification” for lavish overspending also foreshadows similar events that are coming for Lily. The manipulation and tension in her family here hint at the struggles and moral dilemmas that Lily will face as she navigates high society. This flashback sets the stage for the complexities and conflicts that will define her trajectory.