Musician Sly Stone is featured in“ Summer of Soul,” the directorial debut of Ahmir“ Questlove” Thompson.

Musician Sly Stone is featured in “Summer of Soul (...Or, When the Revolution Could Not Be Televised),” the directorial debut of Ahmir “Questlove” Thompson.

There is a moment so powerful, moving and culturally profound in the documentary “Summer of Soul (…Or, When the Revolution Could Not Be Televised)” that I had to stop watching, walk away and pull myself together.

The documentary, which is directed and executive produced by Ahmir “Questlove” Thompson, drummer of The Roots band that serves as house musicians for Jimmy Fallon’s NBC “Tonight Show,” uses recently discovered film from a half-century ago to tell the story of the Harlem Cultural Festival. The series of concerts was held in what is now Marcus Garvey Park in Harlem in the summer of 1969, at the same time Woodstock was getting most of the media attention in upstate New York.

Many of the musical performances are knockouts: Stevie Wonder doing an extended drum solo that has the estimated crowd of 50,000 in the park moving almost as one, Nina Simone pounding her piano as she sings “Backlash Blues,” Sly and The Family Stone taking the crowd higher and higher, and “Pops” Staples working his twangy blues guitar to drive the gospel harmonies of the Staple Singers. On and on it goes for almost two hours in this fabulous production — B.B. King, the Chambers Brothers, David Ruffin, Mongo Santamaria, Hugh Masekela, Gladys Knight and the Pips.

But this isn’t just a concert film. Through interviews with artists and attendees, keen historical analysis and archival film beyond that of the festival, Thompson has created a musically charged social document that captures what it felt like to be young and alive in the summer of 1969, a time of cultural change in music, fashion, politics and, most of all, civil rights.

The moment in the film that best captures that energy, yearning, hope, pain and sense of community among festivalgoers comes when Jesse Jackson, then leader of Operation Breadbasket in Chicago, an economic program aimed at improving economic conditions for Black people, appears onstage talking about the final moments of the life of The Rev. Martin Luther King Jr., who had been assassinated the year before in Memphis, Tennessee. Jackson was with him that day at the Lorraine Motel.

After telling the festivalgoers how much King loved the song, “Take My Hand, Precious Lord,” he called on the legendary gospel singer Mahalia Jackson and Mavis Staples to perform the spiritual. Mahalia Jackson had sung it at King’s funeral.

Showing the performance by these two artists would be enough, but Thompson contextualizes and enriches the music by including part of a current interview with Staples that takes viewers inside the moment.

Explaining that Mahalia Jackson was her “idol,” Staples recalls sitting next to her onstage as the song was being introduced. The older singer, she says, leaned over to her and said, “Baby, Mahalia doesn’t feel so good today. I need you to help me sing this song.”

Staples says standing there with someone she considered her “idol’ looking on and 50,000 persons waiting for her to start the tribute song to King was an “unreal moment” that made her “just want to shout.”

What follows as she starts to sing and is later joined by Mahalia Jackson is some of the most beautiful, moving, spiritual, poetic, pained and sanctified shouting you will ever hear. And while some performances in the film are clipped for pace and time, Thompson has the wisdom to let this performance play out in full as these two musical giants and the inspired musicians playing behind them wring every drop of holy emotion from the song.

Making it a transcendent and perhaps even religious experience is the fact that they are doing it in front of 50,000 people, heads bowed apparently feeling the words of the song and the loss of King as deeply as anyone onstage. Trust me, the performance of this song alone, enriched as it is by current interviews and archival images from the death of the civil rights leader in 1968, is worth whatever you have to pay to see this documentary.

There are lighter moments in the documentary. The famed comedian “Moms” Mabley included material in her performance about America’s moon landing in July of 1969 as the festival was taking place.

“A man’s gone to the moon,” she says, and then pauses to set up her punchline. “I went as far as Baltimore with him, and I got off.”

But even here, Thompson goes a couple of cuts deeper to explore the sociology of the moon landing in terms of race, money and American priorities at the time.

Festival attendees and others in Harlem are shown in archival clips from CBS News and other outlets questioning the nation’s allocation of resources.

“The cash they wasted getting to the moon could have been used to feed the poor Black people in Harlem and all over,” one man says.

“Let’s do something about poverty here,” says another.

Those quotes play over the Staples Singers singing about change. If there is a dominant theme running through the documentary it is the sense of change that was in the air: changes in fashion, hair styles, attitudes and politics. As the film points out, for all the revolutionary change and protests of the 1960s, the facts of that summer were pretty stark: four progressive leaders assassinated during the decade (King, John Kennedy, Robert Kennedy and Malcolm X); the nation still mired in the dirty war in Vietnam; and a Republican who had run on law and order and states’ rights, Richard Nixon, in the White House.

As Simone sings in “Backlash Blues” in the film: “Mr. Backlash, Mr. Backlash, who do you think I am? You raise my taxes and freeze my wages and send my only son to Vietnam. You give me second-class houses and second-class schools. I know you think all colored people are just second-class fools.”

Many Black Americans were saying enough is enough. When New York City police refused to work the festival, Black Panthers took over the policing duties backstage in what was then known as Mt. Morris Park. Black performer after Black performer talks in the film about the special joy and validation they felt at being cheered by the Black audience in the park. That was especially true of artists like Marilyn McCoo, of the 5th Dimension, and Gladys Knight who had achieved crossover success.

The very designation of Black became mainstreamed in American culture in 1969, as journalist Charlayne Hunter-Gault explains in the film. She was then a correspondent for The New York Times.

“For the first time, I wrote Black instead of Negro,” she said, adding that she did so in one of her stories because she had been listening to the people of Harlem who “were calling for the change” in language.

“But some white editor changed my wording from Black back to Negro,” she added. “I was so upset, I dictated an 11-page memo calling for the change.”

Hunter-Gault said the managing editor at the time, Abe Rosenthal, agreed with her memo.

“From the point on at The New York Times, people of color, this color,” she said pointing to herself, “were referred to as Black.”

Ultimately, this is a film about identity and how music both shapes and is a reflection of how we see ourselves and imagine we might be. “Summer of Soul” not only captures that complicated process but also shows how various aspects of popular culture, from fashion to music to religion and politics, intersect at revolutionary moments like the late 1960s to change consciousness.

It’s a blessing that the Harlem Cultural Festival was filmed and that someone saved the tapes even if there wasn’t the interest or money to do anything with them at the time. It’s a double blessing that they were discovered and wound up in the directorial hands of someone as culturally astute, sensitive, skilled and visionary as Thompson.

Maybe the revolution couldn’t be televised in 1969, as the subtitle of the documentary says. But one important part of it that took place in a park in Harlem more than half a century ago can now be streamed on Hulu and seen in theaters.