Catherine Barkley is a static character in the novel; that is, she does not undergo any major transformation over the course of A Farewell to Arms. Apparently she has done her growing and changing before the story began. Hemingway can therefore "use" Catherine as a foil to Henry and an index of his maturation. She is like a constant in a scientific experiment. Of course, this does not make her any less interesting than Henry, and it certainly makes her no less admirable. She's simply less dynamic.
The writer's use of Catherine to contrast dramatically with Henry — to show us just how much learning and growing he has yet to do — begins in the first scene they share together. Henry is still playing childish games: telling her he loves her when he doesn't, for instance. Soon, however, the tables are turned. Catherine not only resists Henry's advances; she reveals that she knows he has been playing a game. Apparently she has been playing one too: "You don't have to pretend you love me," she tells Henry. "You see I'm not mad . . . " Here Catherine proves wiser than she at first appeared — wiser in the ways of the world so far than the easily deceived Henry. Indeed, the latter may be attracted to Catherine precisely because of her aura of hard-earned maturity. Well, that and her hair.
