What is the main theme in Mrs. Bridge?

One of the themes of Mrs. Bridge is the way in which the white middle class in the years between the two world wars (the 1920s to 1940s) tried unsuccessfully to protect themselves from the changing times. India Bridge, the protagonist, is resolutely dull. In fact, the first line of the novel reads, "Her first name was India—she was never able to get used to it" (1). Her name is simply too exotic for her.
India Bridge approaches life without any idea of her goals and dreams. As Connell writes, "She was not certain what she wanted from life, or what to expect from it, for she had seen so little of it" (2). She wants to drift through life as a wife and mother, except reality has a way of poking its ugly head into her mundane existence. For example, Mrs. Bridge's responds to her daughter Corky's friendship with the black daughter of the gardener by realizing that "the girls would drift apart. Time would take care of the situation" (11). She does not confront the situation of racial tension in America in any way except through patient indifference.
Indifference and passivity are her approach to the way the world is changing, but as the world changes, Mrs. Bridge gets left behind. For example, her daughter Ruth informs her that one of the men who works in her office is gay. Mrs. Bridge simply does not understand what her daughter means, and, after this conversation, Mrs. Bridge feels "as isolated as she had ever been in her life" (191). The world and its changing ways simply pass Mrs. Bridge by.