What is the theme in Villette by Charlotte Bronte?

Lucy Snowe's (the name may be viewed as symbolic of the lack of warmth in her nature) problems have been "diagnosed" in various ways by expert readers—in fact, until depth psychology became established, Villette, while meeting with popular success, underwent severe criticism for its unrelieved grimness. Two of the most vocal denigrators were Bronte's contemporaries, Harriet Martineau (an erstwhile friend of Charlotte Bronte), who said the work was "too painful" to read; and the renowned critic, Matthew Arnold, who found it "hideous," "disagreeable," and "convulsed." Today, however, with the advantage of current psychological insights, a number of literary scholars judge the book as Bronte's finest work.