what purpose does chapter 27 serve?

In Chapter 27, Mr. Link Deas is revealed as another member of the forces working for fairness in Maycomb by his defense of Helen against the menace of Mr. Ewell. (During Tom's trial, Mr. Deas stood up and shouted that he had never had a problem with Tom Robinson, and that he was a good worker and a good man. The judge immediately quieted him and instructed the jury to ignore his statements in order to avoid a mistrial.) Meanwhile, Mr. Ewell is again shown to be cowardly and evil, threatening those who can defend themselves least. This chapter continues to provide a building tale of suspense, as the book is clearly coming to a close, and we will soon learn how Jem broke his arm, and the final events the novel has been leading up to. The ordinary and harmless event Halloween pageant develops into an evening fraught with horror.