What is the purpose of the interruption of Gatsby's story at the beginning of chapter 8?The story that is interrupted by the butler.
I think you're talking about the conversation between the gardener and Gatsby that occurs the morning after Gatsby has revealed the truth of his long and sordid love for Daisy to Nick. After breakfast, Nick and Gatsby sit on the porch, and the gardener comes to inform Gatsby that he intends to drain the pool that day.
“I’m going to drain the pool to-day, Mr. Gatsby. Leaves’ll start falling pretty soon, and then there’s always trouble with the pipes.”
“Don’t do it to-day,” Gatsby answered. He turned to me apologetically. “You know, old sport, I’ve never used that pool all summer?”
I looked at my watch and stood up.
“Twelve minutes to my train.”
The gardener's mentioning of draining the pool, and Gatsby's request to change the date foreshadows Gatsby's death. It is also at this point that Nick decides to leave...leave Gatsby alone, with his memories. There's a strong sense of loneliness and melancholy radiating in Gatsby's sentence about never using the pool. It's almost as if he's entreating Nick to stay and swim with him. But Nick leaves, and Gatsby is dead hours later.