Selfishness
Most of the characters in The Barracks Thief are essentially selfish people. They pretend to care about others, but their self-interest is their primary motivation. This greed leads to Lewis's theft of the money from the others in the barracks, as well as Guy Bishop's abandonment of his family to pursue the life and woman he desires for himself. Keith takes off with the car without any thought as to what it might do to his family, and even Hubbard is selfish in his own way; he deserts the army because he doesn't think he wants to do it anymore.
Payback
Payback for wrongs is an expectation in the Army, at least in how it is presented in this novel. When Lewis is caught stealing from the others in the barracks, he is dishonorably discharged as punishment for his actions. The men themselves also take revenge on Lewis, subjecting him to a "blanket party" (throwing a blanket over him and beating him up), and their superior officer turns the other way. Even outside the barracks, revenge is a major theme; out of payback for his father walking out on Philip, Keith, and their mother, Philip leaves his father stuck under a bicycle in the garage, walking out on him. This karma-like cycle of payback is presented as constant throughout the novel.
Rejection
Many of this novel's characters long for friendship and acceptance, but they are rejected by various people. In the beginning, Guy rejects his family in favor of another woman. Philip is rejected by a friend while still at home after breaking a window, and even when he goes off to the army, he has problems with rejection: Hubble, the one person Philips wants to be friends with, shrugs him off like he's just another army bloke. Lewis is always being rejected by his so-called "friends," and he searches desperately for someone to accept him, even resorting to prostitutes, but this doesn't work either, and eventually he is dishonorably discharged and no one hears from him again.
