"The Book of the Grotesque" offers a preamble to what is to happen in the book. This prefatory story brings out topics that include the shallow nature of humanity, double standards, and how individuals conveniently change the rules, and twist them, creating new rules of thumb altogether. This is a demonstration of how hypocritical we can all be. Therefore, "The Book of the Grotesque" already sets up the foundation about the central themes that will be covered in the rest of the stories.
The story also presents the style that Anderson will use throughout the book, which is the exploration of specific individuals as they are challenged with instances where their life philosophies will be questioned. Like in "The Book of the Grotesque", the storytelling style will include the third person narrative "about" an average individual facing a specific situation in a very similar style as the first story featuring the writer, the carpenter, and the issue of the grotesques.
In not so many words, "The Book of the Grotesque" frames and provides the foundation to the style and theme that will be used throughout the other stories.