The story shows a gradual mental breakdown of the narrator. She reveals it in her diary and goes mad by the end of the story. The point of view changes to highlight the narrator’s irreversible insanity.
Detailed answer:
Charlotte P. Gilman wrote The Yellow Wallpaper to demonstrate the harmful effect of forced bed rest on women with mental problems. In the story, the narrator has recently given birth and now goes through a severe psychosis. Her husband is a physician. He believes that she should stay in their rented summer house and avoid any work to get better.
The story consists of a series of diary entries. They show the events from the narrator’s point of view, who describes her feelings and concerns. With the progress of her mental issues, the style changes, too. It reflects the character’s condition. By the end of The Yellow Wallpaper, the entries become shorter and more confused.
As the narrator gets obsessed with the horrible wallpaper, she convinces herself that a woman is trapped behind it. She tears it down, trying to free the mysterious woman. It marks the point of absolute insanity for the protagonist. In her mind, she merges with the woman from the yellow wallpaper. The narrator is no longer able to write diary entries, so the point of view has to shift.