What is the purpose of the novel excerpt from northanger abbey by Jane Austen?

It was one of her first works, so she was trying different styles. On the other hand, Gothic novels are central to the book's plot, that is why this type of literature is quoted frequently. I do not think Austen appreciated it: it must have had too much exaggeration, too much feeling and drama for a woman of her principles and taste (so she indirectly ironised both her heroine and her beloved Gothic literature).