A main book that helps guide the girls and structure the novel is the allegory The Pilgrim's Progress by John Bunyan. The girls each find a copy of it for Christmas—each with a different colored cover—under their pillows. Many of the moral lessons the girls learn as they grow up during the novel are modeled on lessons from Bunyan. Like Christian, the main character in The Pilgrim's Progress, they embark on a "pilgrimage" to grapple with their faults so as to become better Christians. Beth, in particular, likes to quote from this book.
Another significant book is The Pickwick Papers by Charles Dickens. The girls have founded their own Pickwick Club modeled on the club in the novel. They each have taken the name of a character in the novel. Jo, for example, is Augustus Snodgrass, who wants to be a poet: like him, Jo has literary aspirations. Their fascination with Dickens attests to his popularity in this period.
Jo also mentions Uncle Tom's Cabin by Harriet Beecher Stowe. This, too, was a wildly popular book and would fit in perfectly with the abolitionist sentiments of the Alcotts—and, by implication, the Marches.
Beth reads Wide Wide World, a sentimental best seller by Susan Warner with a plucky and morally upstanding female heroine.
Jo also mentions The Vicar of Wakefield by Oliver Goldsmith. Jo secretly reads this novel while Aunt March naps and finds it a more exciting read than Aunt March's preferred reading material, William Belsham's essays. Jo finds these morally instructive essays, which she has to read aloud to her aunt, tedious.
The works the girls mention would all have been very recognized and popular in the Civil War period in which the book is set, adding a layer of realism to the novel.