Charlotte Lucas has been attentive and encouraging to Mr. Collins. One morning he sneaks out to her house and delivers a long-winded marriage proposal. Aware of his shortcomings but wanting stability in her future, Charlotte accepts. Her parents, seeing her fortunes rise so quickly, are thrilled.
Charlotte contrasts with Elizabeth in putting her future financial security before love. She knows that marriage is her only option to guard against a hard life.
Charlotte privately tells Elizabeth that she's engaged, and that all she wants is a comfortable home. Elizabeth is stunned but wishes Charlotte happiness. Afterwards, Elizabeth is disappointed that her friend is humiliating herself, having "sacrificed every better feeling to worldly advantage."
Elizabeth thinks she could never marry just for financial advantage. But the reasons to marry are complicated. Even Elizabeth will later have a strong attraction to Darcy's magnificent estate.