Frederick Wiseman, who can reasonably be called one of the most groundbreaking film-makers still working, has spent his entire career taking deep dives on very specific topics. It’s maybe something of a punchline that now, at age 87, his latest subject is everything.

For over 50 years Wiseman’s all-seeing, fly-on-the-wall cinema has visited institutions (a psychiatric hospital, a park, a museum, a concert venue, a school), gobbled it all up and served it back in an edited form that, while avoiding a traditional three-act structure, links sequences that build to a rich, almost-transcendent understanding. Lord knows others ape the style, but few compare.

Ex Libris: New York Public Library has the drive of a vociferous reader checking out and renewing the maximum number of books their card will allow. Its running time of three hours and 17 minutes is generous enough to succeed on multiple levels. The most prominent theme is the divide between rich and poor, and what the NYPL means in different neighbourhoods. The gorgeous main branch on Fifth Avenue with its marble lions serves a different function than the outposts in the economically disadvantaged outer boroughs. On Fifth Avenue, a “Books at noon” guest like Richard Dawkins will wax about the Enlightenment; off Kingsbridge Road in the Bronx, the community huddles up for job interview tips.

The only recurring characters are the caring and determined administrators (some googling puts faces to names; by and large Wiseman doesn’t care for formal introductions) who agonise over the budget and try to anticipate changes in digital technology. There are side trips to speciality branches, such as Lincoln Center’s Library for the Performing Arts, Harlem’s Schomburg Center for Research in Black Culture, the Mid-Manhattan Library’s fabled picture collection and the Braille and Talking Book Library in Lower Manhattan. Most of the visits focus on a community activity or guest speaker about a panoply of topics (sexual innuendo at Jewish delicatessens, the logistics of deaf interpretation at theatrical events, misguided Marxist defences of slavery among 19th-century southern intellectuals, Gabriel García Márquez) and each one is absolutely fascinating.

Facebook Twitter Pinterest Focus … young New Yorkers pursue tech projects in one of the library’s borough branches. Photograph: Courtesy of Tiff

Ex Libris rolls out like a collection of short films. If you aren’t that into this special event (maybe you just don’t dig slam poetry or watching kids build robots) sit tight because in a few minutes we’re moving on. It’s like watching Wiseman skip along through the stacks of all accumulated human knowledge.

Frederick Law Olmsted is believed to have coined the term “lungs of the city” in reference to Central Park. It becomes quickly evident that the New York Public Library is its mind. But Wiseman’s film delves deeper. A mind isn’t just a collection of facts, as gratifying as the process of learning may be, it houses our understanding of community and morality. Threads reappear and resonate in each of the library’s “lessons” until they vibrate into a basic, essential blur: listen, learn and be kind.

The NYPL administrators are far from the cliche of jaded bureaucrats (and if I ever meet Anthony T Marx, Carrie Welch, Iris Weinshall or Khalil Gibran Muhammad near a checkout desk they can expect an enormous bear hug), but they are understandably humbled by the responsibility of allocating funds to best serve an enormous and diverse group of people. This includes how to most humanely deal with homeless people taking refuge in branches meant to serve an entire community.

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In between the meatier scenes, Wiseman regularly takes a breath to snoop on individuals plugging away at the various branches. In addition to folks like me tapping at a laptop are people scrolling through a century of old newspapers, either for research or just for fun, plus those who play video games, doodle in a notebook, investigate treatments for cancer with an anguished look on their face or maybe just zone out for a breath. More than any other civic institution, it is a place for the betterment of everyone in every conceivable way, and if this ends up being Frederick Wiseman’s last film I can think of no better swan song.