* To establish a descent into madness: The narrator's escalating cruelty towards the cat, from mere irritation to outright violence, shows a gradual loss of control and a descent into a darker, more violent state of mind. The buildup emphasizes this mental deterioration, preparing the reader for the ultimate act of violence.
* To highlight the contrast between the narrator's initial affection for the cat and his later hatred: The narrator initially loves the cat and describes it with fondness. This initial tenderness serves to highlight the shocking and disturbing nature of his later actions. The contrast between the two drastically different states of mind underscores the narrative's theme of the destructive power of unchecked rage and cruelty.
* To create suspense and foreshadowing: The narrator's growing obsession with the cat, his paranoia, and his strange behavior all build tension and foreshadow the inevitable act of violence. The reader is aware that something terrible is going to happen, creating a sense of dread and anticipation.
* To explore the nature of guilt and remorse: The buildup allows the narrator to fully detail his internal struggle with guilt after the act. The reader witnesses the gradual progression of his guilt and the gradual breakdown of his sanity, making the narrative even more chilling and psychologically disturbing.
In essence, the buildup serves to create a psychological portrait of a man driven to madness by his own dark impulses. The act of killing the cat becomes a culmination of this descent, highlighting the dark potential that lurks within the human psyche.