Economic effects on human relationships
Gregor is enslaved by his family because he is the one who makes money. Thus, with the possible exception of his sister, the family seems to treat him not as a member but as a source of income. When Gregor is no longer able to work after his metamorphosis, he is treated with revulsion and neglected. Once the family begins working, they also find difficulty communicating with each other, eating dinner in silence and fighting among themselves. The exhaustion of dehumanizing jobs and the recognition that people are only valuable so long as they earn a salary keeps anyone who works isolated from others and unable to establish human relations with them.
Family duty
The theme of family and the duties of family members to each other drive the interactions between Gregor and the others. His thoughts are almost entirely of the need to support his parents and sending his sister to the Conservatory. Though Gregor hates his job, he follows the call of duty to his family and goes far beyond simple duty. The family, on the other hand, takes care of Gregor after his metamorphosis only so far as duty seems to necessitate. He is kept locked in his room and brought food. In the end, his room is barely cleaned and his sister no longer cares about what food she brings him. Her actions are routine, as she only wants to do enough that she can claim she has fulfilled her duty. When she decides she has had enough, she insists that their duty to him has been fulfilled: "I don't think anyone could reproach us in the slightest," she says as she suggests that they need to get rid of him.
Alienation
Before his metamorphosis, Gregor is alienated from his job, his humanity, his family, and even his body, as we see from the fact that he barely notices his transformation. In fact, even his consideration for his family seems to be something alien to him, as he barely notices it when he loses this consideration at the end. After his metamorphosis, Gregor feels completely alienated from his room and environment and, as a symbol of this, can't even see his street out the window. The Metamorphosis, then, is a powerful indictment of the alienation brought on by the modern social order.
Freedom and escapism
Gregor is trapped in his job by his duty to his family, but he dreams of the day when he can finally pay off their debts and quit his job. His need for freedom from the restrictive demands of work is expressed in his metamorphosis, by means of which he escapes. This escape, however, fails to bring Gregor freedom, for he is now imprisoned by his family in his room. Thus, when Gregor works, he is enslaved by his job and, when he doesn't work, he is enslaved by his family. There is no way of balancing out freedom and duty, and in the end one is always a slave. The only means of escape turns out to be death.
Guilt
Guilt stems from family duty, and is Gregor's most powerful emotion. When he is transformed into an insect, Gregor is made unable to work by circumstances beyond his control. Despite the fact that his metamorphosis is not his fault, however, he is racked by guilt every time that the family mentions money or that he thinks about the pain that he has inadvertently inflicted on them by losing the ability to support them. Guilt, it turns out, is deadly, as Gregor realizes at the end that his life is the only thing keeping the family from a better life. He dies for them just as he lived for them: out of guilt.
Personal identity
Alone in his room, Gregor tries to rebuild the self-identity that he had lost by living entirely for others and ignoring his own needs. He cannot, however, escape from what he sees as his family duty, and continues to act only to serve his family by doing his best not to inconvenience them. Gregor's comments about his family's behavior are often tinged with resentment at the way they treat him, but he will not allow himself to recognize his bitterness. Gregor manages to escape his self-effacing sense of duty only in the last chapter, when he asserts himself in realizing that his family has been neglecting him. Gregor's search for his identity seems hopeless, however, because he never had an identity to start with. He finds his humanity only at the end, when his sister's playing reminds him of his love for his family. This love, coupled with his freedom, is the final ingredient he needs to establish his identity.
