Although he is the most disliked character in the book, C.S. Lewis includes Eustace in this novel for a very important purpose: he is an outsider. Eustace's importance is established almost right away, because the opening of the book begins with "There was a boy called Eustace Clarence Scrubb, and he almost deserved it." This sets up not only a character that is essential to the understanding of the book, but also foreshadows that his character would be a nuisance throughout.
Eustace is the epitome of a character on a journey that represents an outside perspective. Calvino, Hau'ofa, and Wendt all used similar figures. Lewis creates a character like this in each book of the Narnia series, to give the perspective of an outsider. For those who are familiar with The Lion, The Witch, and The Wardrobe, they would know that Edmund's first experience in Narnia was quite traitorous. Instead of helping those in need he fell into the temptations of the queen. He feasted all day on Turkish Delight and gave away his siblings. Eustace's first experience is similar, because he does not appreciate the true value of this fantasy world. Eustace is constantly bitter even among a crew of happy travelers. He exaggerates the problems and constantly compares everything to his life back home. Eustace represents the typical traveler who is not prepared for a journey to a new place, and does not appreciate the value of such a trip. However, as the novel continues and Eustace goes through changes (both physical and spiritual), he is able to finally appreciate Narnia.
Just as Eustace changes as the novel progresses, so does the reader. For people familiar with the Narnia series or other similar books, they enjoy another great fantasy novel and may appreciate the underlying meanings. Those who "have not read the right kind of books" are now immersed in the world of fantasy. They would now know what a dragon is, for instance, just like Eustace. Lewis wrote this series for those who love fantasy, but also as an opportunity to expand the minds of those who only read mystery novels. By extension this can be applied to the world of travel. Often people will travel to a foreign place and immediately devalue the experience. However, all it takes is for that person to look at their own reflection and realize the truth, just like Eustace. The voyage of Eustace in this book shows that there will always be people who do not immediately see eye to eye with the others, but an open mind can reveal what is meaningful even to an outsider.