How does Edith Wharton explore the theme of marriage in The House of Mirth?

Wharton explores and critiques marriage primarily through her main character,  Lily Bart. Lily is beautiful, gracious, intelligent and has been raised in high society, but has very little money. She has been groomed for one destiny alone, to make a "good" marriage. A good marriage involves wedding a wealthy man of her social class. While she "was beginning to have fits of rebellion" against this path, and while "she longed to make an independent life...

Wharton explores and critiques marriage primarily through her main character,  Lily Bart. Lily is beautiful, gracious, intelligent and has been raised in high society, but has very little money. She has been groomed for one destiny alone, to make a "good" marriage. A good marriage involves wedding a wealthy man of her social class. While she "was beginning to have fits of rebellion" against this path, and while "she longed to make an independent life for herself," Lily simply cannot overcome her social indoctrination of seeing marriage as the only legitimate "career" goal for a woman. Much of the novel explores her struggle with this. She sees that married society women, like Judy Trenor and Bertha Dorset, wield a great deal of money, power and status through marriage. Lily wants that, but she also has a sense of integrity that prevents her from jumping heedlessly into a loveless marriage just for money and status. 

Lily is trapped between her own integrity, which society does not encourage her to develop, and her desire for a rich, comfortable, easy life. For example, Wharton explores  the dilemmas the marriage market creates for Lily's integrity as she is on the verge of snagging the wealthy Percy Fryce, but veers away from him because she doesn't love him and doesn't merely want to manipulate him into marriage.

Wharton does depict at least one woman, Gerty Farish, who is single and finds success as a social worker. Wharton's prmary marriage theme, however, shows that being trained, as Lily was, to sell yourself on the marriage market warps and destroys women.