What is the main theme in the novel, Gentleman's Agreement?

Gentleman's Agreement delves into the imperfections of society, specifically the prejudices of the American mainstream in the 1940s. Keenly aware of subtle forms of discrimination, she describes the latent anti-Semitism rampant in America. Hobson focuses on people who do not regard themselves as anti-Semites, and who deny charges of bigotry with the familiar rationalization that "Some of my best friends are Jews." Hobson attempts to show that many of these people are enemies of the Jews as much as are overt antiSemites.