What is the theme in Seize the Day by Saul Bellow?

Alienation and loneliness are themes in this book. Tommy Wilhelm's sense of estrangement not only from his own family but also from his acquaintances and the entire city of New York places the themes of alienation and loneliness at the core of the novel. From the novel's opening scene, in which Wilhelm talks briefly with "Rubin, the man at the newsstand," it is clear that these men know many things about each other, and yet "None of these could be mentioned, and the great weight of the unspoken left them little to talk about."