How does the act of metamorphosis relate to theme of Kafka's The Metamorphosis?
In Kafka's The Metamorphosis, Gregor has been supporting his family for years. Unfortunately, his family has little appreciation for his hard work—a life of drudgery that he hates—which allows his family to live a comfortable life of leisure.
When Gregor Samsa wakes up on this rainy morning, he has turned into a large bug. Gregor reflects as to how he has ended up this way. He considers difficulties he faces, which he believes might be the cause of his present trouble.
“Oh God,” he thought, “what a strenuous occupation I've chosen! Always on the road, day out, day in. The rigors of the job are much greater than if I were working locally, and, furthermore, the nuisances of traveling are always imposed upon me—the worries about train connections, bad meals at irregular intervals, fleeting human contact that is ever-changing, never lasting, and never expected to be genuine.”
Gregor hates the job but still goes. He never complains that he is the only one at home who works. What seems particularly significant, however, is his lack of connection to others: he mentions that his contact with other "humans" (interesting that he makes this distinction) is short-lived and that he is never able to remain in one place long enough to make any friends. In essence, Gregor is very much alone. This introduces one of the story's main themes: alienation and loneliness.
When Gregor becomes a giant insect, if we take this literally, it reflects yet another way in which he is isolated from the world. Even as a bug, he still imagines trying to catch the train—he fails to instantly realize that his life is over as he has known it. Gregor is so programmed to provide for his family that he considers every option possible so that he can continue to do so. This reflects another theme: "isolation and self-sacrifice." Gregor has made no friends because of his work and does not have a girlfriend. He has been closer to Grete—but she ultimately betrays him. He has sacrificed his happiness for his family's.
Another important theme, “father-son antagonism,” is introduced in face of Gregor's metamorphosis. Till now, Gregor's family members have been like parasites, living off of Gregor's hard work and misery. They show him no love or appreciation. He is isolated at work and at home. Once Gregor cannot work, his father makes no effort to hide his resentment of his son—in fact, he physically attacks Gregor because he is no longer useful to them.
[Gregor's father] had filled his pockets from the fruit bowl on the credenza, and now, without aiming precisely, threw apple after apple...One weakly thrown apple grazed Gregor's back but slid off harmlessly. One direct hit that flew immediately afterward penetrated Gregor's back...and...he felt like he was nailed down and stretched out, all his senses being completely confused.
Finally, we can see Gregor's transformation as a way for him to escape: there is no way he can work now. The expectations of his family cannot be forced on him. As an insect, Gregor enjoys scurrying across the floor, even hanging from the ceiling, but his is not a family that will go out of its way to help him. His mother saves his life once; his sister cares for him for a short time. Forced to do for themselves, they find ways to survive, but they abandon Gregor, who eventually dies.
While change in the Samsa house is necessary and galvanizes the family to assume responsibility, Gregor's metamorphosis costs him his life.