Most of Santopietro’s work is given over to that movie — so much so that I began to wonder if this book was intended to be a cultural history of the adaptation alone. Santopietro has previously written books about other beloved film adaptations, including “The Sound of Music” and “The Godfather”; here, he details everything from the producers, the screenwriter, the cast and the set decorators to how the film was received by the critics, the public and Lee herself. He is passionate about Gregory Peck as just the right kind of leading man to step into the role of Atticus, and shares a great deal about the process of selecting the child actors to play Scout; her brother, Jem; and their friend Dill. Santopietro goes so far as to elaborate on the lives of everyone involved in the film for years after its release. All of this material is vaguely interesting, but the author fails to explain how it supports his argument that “To Kill a Mockingbird” matters.

On top of that, the book’s structure is strange. There are all kinds of digressions in each chapter, some of which feel more like information dumps than components of a cohesive narrative. Nor is there a clear progression between them: The 11th chapter is about the merits of the movie as an adaptation, and the 13th is about Harper Lee’s private nature, but the 12th asks the question: “Is ‘To Kill a Mockingbird’ Racist?” (My answer to that question is yes.) These organizational choices — and the one or two jarring Stephen Sondheim quotations he cites — are bewildering. As much as I admire the exhaustive research, not a lot of care seems to have been put into how it is conveyed.

Not until the last few chapters does Santopietro finally try to make a definitive case for the importance of this seminal American novel. He offers statistics about the book’s commercial success: “Translated into 40 languages, the novel sells approximately 750,000 copies every year,” he writes. “In total, some 40 million copies have been sold worldwide since 1960, and at the time of Harper Lee’s death in 2016, her annual royalties remained in excess of three million dollars.” Few other books have sold so robustly for so long. “Mockingbird” is also required reading “in over 70 percent of American high schools.” These numbers are impressive indeed, but ubiquity and quality are not the same thing (and neither one is necessarily the same thing as importance).

Santopietro also notes that we’re still living in a world where ethnic prejudice abounds, not just toward black people but Mexicans, Syrian refugees and others. The author is not ignorant of the racial zeitgeist, but it is odd that he thinks Lee’s novel speaks to it adequately. He boldly claims, “‘Mockingbird’ succeeds in a basic task of literature: the expansion of worldviews by means of exposure to differing communities and cultures.” In that it tells the story of a wrongfully accused incarcerated black man, he is correct, but it is important to question just what kind of exposure the text offers. Given the shallowness of the black characters — how they are vehicles for Scout’s story instead of their own — we as readers should raise the bar higher than mere “exposure.”

Santopietro saves his keenest observation for the final pages of “Why ‘To Kill a Mockingbird’ Matters,” in which he acknowledges the power of nostalgia: “The continued heartfelt response to ‘Mockingbird’ now seems inextricably tied up in Harper Lee’s ability to underscore a sense of community sorely lacking today.” He goes on to discuss how people spend too much time in isolation with their electronic devices, as neighborhoods, communities and communication disintegrate. He acknowledges how much the culture has changed since the book’s publication in 1960, but laments the proliferation of “dark and damaged characters”on television and in film. What he conveys most powerfully is a yearning for a simpler time — a uniquely white yearning, because it is white people to whom history has been kindest. It is white people who seem to long for the safety of cloistered communities where everyone knows one another, where people know their place and are assured of what their lives may hold. Clearly, Santopietro identifies more with Scout, Jem and Dill than with, say, Boo Radley, the town recluse who probably wouldn’t yearn for that simpler time when the townspeople regarded him with open distance and mistrust.

And then the author illustrates why it is hard to take this book seriously: “The United States found in ‘To Kill a Mockingbird’ was unquestionably a more racist, oppressive America, deaf to the desires and hopes of women, homosexuals, minorities and nearly anyone who did not fit the prevailing definition of ‘normal.’” This statement is technically true, but it overlooks the serious racial tensions our nation still faces. Santopietro does make brief mentions of President Trump and his lack of leadership during the Charlottesville riots, as well as of the responses (or lack thereof) of black people to “Mockingbird,” but these asides feel tacked on and unexplored. The groundwork for “Why ‘To Kill a Mockingbird’ Matters” is astute, but the intellectual analyses are not, and the book suffers for it.