A Note on Edith Wharton's The House of Mirth
The point of The Age of Innocence is that one can either find a sort of salvation in accepting fate and duty or succumb to despair and resentment. The House of Mirth speaks of a closely allied theme. It's theme is the goal of creating a "republic of the soul," the orchestration of one's dispositions such that one isn't swept hither and thither by them, driven to extremes by compulsion and for lack of a central control. Whereas the former book's Countess Olenska acheives this harmony and control and Newland Archer does not, in the latter book Lawrence Selden enjoys the repose and Lily Bart fails to acheive it. In the latter case, however, the failure is much more grim in ramification than in the former case. At least Archer escapes with his life.
Lily Bart sees Selden's republic of the soul. It is palpable for her. She begins to create it in herself whenever he is near enough to her for her to observe his manner. But contact with another isn't enough to develop one's own virtue. The point is not that Lily doesn't develop virtue; it is that she could have done so. As does Archer in The Age of Innocence, Lily fails because she sees herself as mastered by fate, rather than as fate's equal.
In both books, Wharton wants the reader to see that virtue is crucial and failure to acheive it is failure to acheive a sort of salvation. The House of Mirth paints this picture more starkly than Archer's "mere gray speck of a man." Lily Bart loses everything.
Selden, for his part, fails, as well. Sometimes virtue requires action that would in most circumstances seem somehow rash or wide of the mean. Selden mistook passivity for equanimity at crucial moments where more forthright action would have made all the difference, both to himself and to Lily.