The central theme of The Red and the Black is the ambition of a poor young man in a society that closes its doors to those not born in the right place, and the price that this ambition exacts. Julien Sorel calculates every step and discovers, only in prison, that he was happy in the few hours when he did not calculate.
Around this axis the other themes run. Hypocrisy is the method, and the narrator names it already in Chapter V, calling it "this horrible word." Social class is the ruler: Verrières measures everything by "PAYS OFF," and Paris measures by birth and manners. Love appears in two opposite forms, that of Madame de Rênal, who loves without knowing that she loves, and that of Mathilde de La Mole, who decides to love.
Politics, finally, decides the rungs of Julien's career, from the seminary to the jury. The subtitle, "Chronicle of 1830," warns that the subject is France at that moment, and the narrator himself interrupts the story, in a feigned dialogue with a publisher, to discuss whether politics belongs in a novel. The publisher replies that without it, the characters would cease to be Frenchmen of 1830.
The book does not condemn ambition as a simple vice. It shows that ambition occupies the place where happiness would be: Julien calls a raise wrested from his employer a battle won, and, a lieutenant for two days, he already calculates the next rank. In prison, he wonders that he only learned "the art of enjoying life" when he saw the end approaching.