Imagine realizing that, well before reaching the age of 40, the work that will likely be remembered as your legacy is already in the past. Tony Kushner was just 36 when he wrote “Angels in America,” his seven-hour, Brecht-on-steroids epic of AIDS, Mormons, Roy Cohn, drag queens, Bolsheviks, and, yes, angels in Reagan-era America. That’s the same age George Gershwin was when he composed “Porgy and Bess” and a year or two older than Edward Albee and Arthur Miller were when they wrote “Who’s Afraid of Virginia Woolf?” and “Death of a Salesman,” respectively.

I saw Mr. Kushner address this sobering idea at a speech in Chicago in 1994, a year after “Angels” landed on Broadway, and he suggested at the time that the only solution was to shrug off the idea and push forward. Despite its title, Freida Lee Mock’s documentary “Wrestling With Angels: Playwright Tony Kushner,” which makes its premiere tonight, doesn’t really tackle this issue of “Now what?” But this energetic and engrossing work clearly shows that Mr. Kushner, who hears a “kachunk” every time a new play begins to surface in his mind, has kept on pushing.

Mr. Kushner often talks about his urge to write “left-progressive” art, and the progressing part is on full display here. Ms. Mock essentially depicts his life as a never-ending shuttle between lecterns and laptops, one in which he’s either delivering one of his much-admired public addresses — generally in conjunction with some sort of tribute — or writing.

Interestingly, Ms. Mock — whose documentary on Maya Lin won an Oscar in 1994 — doesn’t show either of these public roles to particularly strong advantage. No matter how many hotel ballrooms or college quads Mr. Kushner hits, his speeches are far better known from the transcripts that get e-mailed and occasionally published afterward.

These dense yet forceful addresses have a power on the page that Mr. Kushner — who generally stares intensely at his notes and looks very eager to leave the podium — rarely conveys live. The sheer intelligence of this material generates its own energy in person, as anyone who’s seen him speak can attest, but little of that passion carries over to the screen. (His extemporaneous remarks, however, are a thing of wonder, something Ms. Mock wisely captures on several occasions.)

Clips from his actual works, meanwhile, are brief and disappointing. “Homebody/Kabul,” which was set partly in Afghanistan and opened just three months after 9/11, draws its strength from the cumulative force of the title character’s mammoth Act I monologue, only seconds of which are displayed here. “Angels” is boiled down to a few clips, most of them from the HBO movie version; the visually resonant moments — the Bethesda Fountain finale, a seraphic Emma Thompson crashing through the ceiling — get priority over those showcasing Mr. Kushner’s refulgent language.

The Holocaust-era children’s opera “Brundibar,” Mr. Kushner’s collaboration with Maurice Sendak, gets similarly short shrift. Ms. Mock spends a bit more time on “Caroline, or Change,” largely because the musical’s autobiographical content helps to fill in some of the blanks in Mr. Kushner’s childhood. The middle, most satisfying third of “Wrestling With Angels” is devoted to his family life, primarily a father who only belatedly came to terms with Mr. Kushner’s homosexuality.

The treat for many theater buffs will be snippets of two smaller, lesser-known works: a discursive homage to the Jewish women in Mr. Kushner’s family and an antiwar piece involving a tormented Laura Bush. As each of these plays makes clear, his art and his politics are never far apart: Oskar Eustis, a longtime collaborator and currently the artistic director of the Public Theatre, bolsters this idea with the intriguing claim that both theatre and democracy were invented in the same place and in the same decade, rendering them forever intertwined. Among the film’s final images are ones of Mr. Kushner on Election Day 2004, struggling to get one voter at a time into a Florida polling site.

Mr. Kushner — who studied at NYU under Carl Weber, one of the core members of Bertolt Brecht’s Berliner Ensemble — states that his goal is to make “left-progressive art that reaches lots and lots of people.” The film ends in 2004, before production had begun on his translation of Brecht’s “Mother Courage,” which premiered this summer in Shakespeare in the Park, or on his Oscar-nominated screenplay to Steven Spielberg’s “Munich.” Even so, theatre buffs might wish that those “kachunks” visited Mr. Kushner a bit more often: Not counting the various adaptations and translations, he hasn’t written a new work since 2003’s “Caroline,” and nothing appears to be imminent.(“John Box Brown,” a piece about slavery and the British textile industry, has been in the works since 1996.)

But “people have an appetite for the difficult,” Mr. Kushner states near the end of “Wrestling With Angels,” and difficult takes time. So does being an intensely committed, perpetually sought-after, endlessly quotable, seemingly inexhaustible citizen of the world. At the rate he’s going, who knows? Those Miller and Albee fellows weren’t exactly tapped out after their early efforts.