Answer:
Moving the story forward and increasing dramatic tension.
Step-by-step explanation:
In the "Metamorphosis" Gregor sansa's whole family depends on his work to survive, so they trusted him, supported him. Strangely, even more than that: they parasitized him, making him a slave to work. Until the day he woke up turned into an insect. From this physical metamorphosis, family life suffers a huge shake.
Having as its starting point the metamorphosis of Gregor, Franz Kafka's novel deals with other transformations. Gregor's entire family was dependent on their work, but with the new situation they are forced to work.
Gregor's entire family begins to change from him from that moment on. For his father, Gregor becomes a "deadweight," worthless. To the mother, object of revulsion. For the sister, loving even after the transformation, also becomes a hindrance. Now he was the parasite.
This change in the Sansa filia moves the story forward and increasing the dramatic tension. This makes the author apprehensive and curious about what will happen in the plot.