Because it is the first it will not go to chapter 2 if it doesn't have chapter 1... It is important because it is the start of the novel... like cooking rice the rice will not cook if there is no water... first pour water before it will be cooked..
It can show whom ever reads that book the writing stye, the word complexity, the theme of the book, that's why for a book, I would have a prologue, one that overviews the story.
