[Graham's] universe was lonely and arid, and [Audra’s] was densely populated with armies of friends and acquaintances.
-- Narration (chapter 1)

Importance: This sentence appears in the first paragraph of the novel, and it quickly establishes the main difference between Graham and Audra. Graham is reserved and introverted, while Audra is extremely extroverted and deeply values making and maintaining friendships.

Cold, hard, perfectionistic. Her favorite drink was a gimlet, and she was not unlike a gimlet herself, in either sense of the word.
-- Narration (chapter 1)

Importance: This sentence helps to establish Elspeth's character and personality. Like Graham, she is reserved. However, her reticent nature appears to stem from a sense of general coldness. Graham's reticence appears to be from a sense of anxiety.

She hates us…We’re not her friends anymore, we’re one of them again: the cheaters, the trollops, the bastards.
-- Audra (chapter 2)

Importance: Audra says this after they learn that Berntrup has left Audra for another...