Though the first sentence tells us that Gregor has turned into some kind of insect, we are never explicitly told why or how this transformation takes place. Or . . . are we? I mean, what and who else changes throughout the story, and how might their changes explicate Gregor’s transformation, abasement, and death?
If one interprets the writing of The Metamorphosis as a form of expressionism, the transformation of Gregor Samsa into a huge insect is a fantastical expression of punishment and salvation from isolation and guilt. As a traveling salesman, Gregor has been alienated, sleeping in different rooms each night, working alone; further,he feels guilty for destroying the dynamics of his family. For instance, his relationship with his father is inverted as Gregor resides as the head of the household and the main breadwinner. Subconsciously, his father resents being displaced--he later wears his uniform of a messenger all the time out of a sense of "perverse obstinancy"--while the mother and sister expect too much from Gregor, expectations that lead to their resentment of him. "What a life. So this is the peace of my old age," the father complains.
Gregor's transformation into the "monstrous vermin" that becomes odious to his family leads to his estrangement from his family, their rejection and his abasement, and, ultimately, death. This death is effected by his repulsive and burdensome presence in the home where the family must hide him from their boarders, and Grete must care for him. Further, his repugnant and looming presence reminds the father constantly of their troubled relationship and his failure as patriarch, so he pelts Gregor with apples, one of which lodges painfully in Gregor's back and leads to his death. When he is drawn to Grete's musical performance before the boarders, he is seen by the three men and thereby embarrasses his sister and ruins the evening. Grete retaliates against him through her neglect. This signifies that artistic sensibility has no place where material concerns override emotional expression. Thus, the tragedy of this novella evolves from the transformation, not only of Gregor in his guilt, but also in the other family members who take advantage of his defenselessness. For, as one critic writes, Gregor is "offensive in appearance, but defenseless in fact."