What is the importance of Sophie in the Chrysalids?
Sophie is an important character because she is David's, and the reader's, first introduction to a Deviant. Waknuk society drills into young people's minds that Deviants (people with genetic abnormalities) are practically sub human. It's for that reason that Deviants are either killed or kicked out of Waknuk society. But from Sophie, David sees that she is every bit as human as he is. Sophie illustrates to David and readers that a person's value is not determined by their genetic structuring or their outward appearance. That's the most important function that she serves in my opinion.
Sophie is also important to the plot of the novel too. After she and her family escape to the Fringes, she ends up being pivotal to David's and Rosalind's survival. She frees them from the Fringes prison and helps them to escape. Without Sophie, David and his group of telepaths never would have been united with the Sealand woman.