Hypocrisy is Julien Sorel's method for rising in a society that does not want him. The narrator names it from Chapter V of Book One onward, when Julien enters the church because he judges that it "would be useful to his hypocrisy."
Julien knows the New Testament in Latin by heart without believing in it, hides a portrait of Napoleon in his mattress at the house of a royalist mayor, and feigns a vocation he does not have. In his mind, the idea of religion is tied to "hypocrisy and the hope of making money." At the seminary, pretense becomes daily discipline. In Paris, Prince Korasoff teaches him what he calls "the only religion of the age": always doing the opposite of what is expected.
But the book does not show only Julien pretending. Verrières lives under the tyranny of opinion, the young bishop of Agde rehearses his blessings before the mirror, Madame de Rênal learns to pretend in order to save her lover, and Mathilde loves according to "a model that was imitated." Hypocrisy is the language of the age, and Julien, alone in his cell, still surprises himself thinking like a hypocrite: "Oh, nineteenth century!"
Julien's true moments are those that escape it: under the linden tree, when he forgets to pretend, and in the mountain grotto, where he feels free. At the end, he refuses to convert "with a show" in order to obtain forgiveness, and he tells Madame de Rênal all his weaknesses. Hypocrisy gave him his career and cost him his happiness.