Harper Lee’s To Kill a Mockingbird illuminates the racism and prejudice that pervaded American society in the 1930s, some twenty or thirty years before the civil rights movement began in earnest.

The story is set in Maycomb, a fictional Southern town where people are resistant to change. Though the inhabitants of this small town necessarily live out their lives in close proximity to one another, a myriad of factors, including race, heritage, and wealth, form a complex social hierarchy within the town. Segregation separates the town along racial lines, but rigid social distinctions govern relationships within Maycomb’s white community as well. The well-to-do may live near and frequently interact with the town’s working-class and impoverished members (as seen in Scout’s classroom), yet the divisions between these groups remain rigid.

It is suggested that this unyielding hierarchy stems from the instinctive desire of individuals in every class to believe that they are superior to others, which creates complex status relationships that extend beyond the traditional socioeconomic and racial sphere. For example, the Cunninghams feel justified in looking down on the Ewells—although they are both poor, white families—because the Cunninghams’ well-known pride and independence garners them greater respect in the town. As Jem observes, 

The thing about it is, our kind of folks don't like the Cunninghams, the Cunninghams don't like the Ewells, and the Ewells hate and despise the colored folks.

Poor, rude, and hostile, the Ewells are despised by most of the town and thus occupy one of the lowest rungs on the social ladder. However, due to the rampant racism in Maycomb, even the Ewells are considered to be socially superior to respectable Black individuals like the Robinsons. The Ewells are aware of this fact and exploit this bias to their advantage in accusing Tom Robinson. Though Bob Ewell is aware of Tom’s innocence, he also knows that as a white man, it is he, not Tom, who will have the town’s support—regardless of how unpopular he is. The hollowness and hypocrisy of Maycomb’s strict social hierarchy ultimately highlights the truth of a key lesson expressed in the novel: “There’s just one kind of folks. Folks.”

Narrated by a young woman recalling her childhood, To Kill a Mockingbird is a bildungsroman, or a coming-of-age story. Through the memories and reflections of an adult Scout, readers follow Scout; her brother, Jem; and their friend Dill as they grow up and learn to navigate the difficulties of coming of age in a changing society. The children are surrounded by conflicting attitudes, particularly with regard to race and class, and must decipher for themselves which ones to adopt as their own. The children don’t undertake this journey completely alone, however; and many of the adults closest to the children—including Atticus, Calpurnia, and Miss Maudie—act as strong moral role models, helping to guide the children toward integrity and away from cynicism, even in the face of terrible injustices.

The book’s title comes from the notion that “it’s a sin to kill a mockingbird,” which is referenced by multiple characters in the book. The underlying explanation of this rule—that it is wrong to harm the innocent—is one of the primary messages of the work. The most clear parallels to the titular mockingbirds are Tom Robinson and Arthur “Boo” Radley, both of whom, like mockingbirds, are innocents harmed by the harsh ignorance and prejudices of the town. Tom's race makes him an easy scapegoat in a town mired in racism, which Atticus refers to as “Maycomb's usual disease.” In sharp contrast to Bob Ewell, Tom is a kind man who cares about helping others. This compassion ultimately leads to his downfall when Mayella (on the orders of her father) falsely accuses him of rape after her father witnesses her unsuccessful effort to seduce Tom. Prior to the trial, few people in Maycomb consider that a Black man accused by a white woman might be innocent, and even after Atticus proves Tom’s innocence beyond a doubt in the courtroom, his guilty conviction is all but assured.

Boo Radley is yet another symbolic mockingbird—he, too, is prejudged by the people of Maycomb, though the prejudice faced by Boo stems from hurtful speculation rather than racism. Boo’s reclusiveness causes rumors to circulate until he is considered little more than a neighborhood pariah. The children regard him as they would a mythical monster or ghost, believing him to be a vengeful perpetrator of various crimes. In reality, he is a quiet and painfully shy man whose reclusiveness is perhaps partly due to his overbearing and dominant brother. Boo shows his true nature in his interactions with Jem and Scout: unbeknownst (at first) to the children, Boo mends Jem’s torn pants, leaves presents for them in the knothole of a tree, places a blanket around Scout during the fire, and saves Scout and Jem’s lives when Bob tries to kill them.

As the children grow up, they find that their initial perceptions about their world and the townspeople are frequently challenged: Boo turns out not to be the “malevolent phantom” they feared, but a mild-mannered, introverted man of great courage and respect. Mrs. Dubose is not the evil witch she appeared to be, but instead a woman determined to die with dignity. Dolphus Raymond is not a worthless drunkard, but instead a man who finds a way to live in a society that judges unfairly. These experiences, reinforced by Atticus’s insistence that “you never really understand a person until you consider things from his point of view,” help the children learn to lead with compassion and refrain from judging others. Keeping an open mind allows the children to develop into stronger moral citizens and ultimately prevents them from becoming jaded when they are confronted with the cruelest aspects of humanity, such as Tom Robinson’s guilty conviction and Bob Ewell’s attack. Though these traumatic events are difficult for the children, particularly Jem, to reconcile, the ability to look for the good in those around them helps the children face the harsh realities of the adult world without losing faith in humanity. Indeed, the book ends on a hopeful note, as Scout mentions that a character in The Gray Ghost had unexpectedly turned out to be “real nice,” to which Atticus responds, "Most people are, Scout, when you finally see them.”