It’s likely that Amir Bar-Lev was the only Grateful Dead fan thinking about Martin Buber and Abraham Joshua Herschel while grooving to “The Other One” and “China Cat Sunflower.”

“Martin Buber has this notion of a genuine encounter with another person being a means of attaining something transcendent,” Bar-Lev explains. “The Grateful Dead was, for me anyway, a way of having an ‘I and Thou’ experience with other people.”

Born in Detroit and raised in Berkeley, Bar-Lev got into the Bay Area band’s music and ethos when he was 13. A little over a decade later, following his acclaimed 2000 filmmaking debut, “Fighter,” in which he accompanied two opinionated Czech Holocaust survivors back to Theresienstadt, Bar-Lev decided his next film would be about the Grateful Dead.

“It had never been made, for one thing,” he recalls. “I knew that somebody was going to make it at some point, and I felt that I should be that person. Also, my formula in a film is never really about what it sounds like it’s about. The Grateful Dead is one of those stories. There’s a superficial way of thinking about the Grateful Dead, and there’s some deeper things involved worth talking about.”

Bar-Lev adds with a smile, “You come for the acid and the hedonism, and you stay for the interesting ideas about pluralism and life and death.”

He had to put his original plan on hold, but in the intervening 15 years Bar-Lev’s reputation grew through his high-profile docs “My Kid Could Paint That” (about the controversial success of a 4-year-old artist), “The Tillman Story” (a damning investigation into the death in Afghanistan of an NFL player from San Jose who enlisted after 9/11) and “Happy Valley” (a portrait of the Penn State community during the arrest and trial of a football coach for child sexual abuse).

Bar-Lev has finally finished his history of the Grateful Dead and their followers, “Long Strange Trip,” and it’s an immersive saga that spans four full hours. Crammed with fascinating details, live performances and provocative themes, it also contains — like every Dead show and most Dead albums — bits and digressions that only the most devout fans will treasure.

“Long Strange Trip” screens Sunday, May 14 in the new DocLands festival in Mill Valley and May 25 at the Clay before debuting June 2 on Amazon Prime Video.

“I know Jews do a lot of talking about the Jewish aspects of Deadheadism,” Bar-Lev said during an interview in San Francisco last month when “Long Strange Trip” played the S.F. International Film Festival. “But I’m always interested in mitigating our human impulse to be tribal by trying to get down to what values are embedded in the thing. As an American Jew making a film about Deadheadism, there’s three tribes right there. I don’t want to wave the banner of anything because the thing I love about all of those tribes is they’re about more than just the tribal affiliation.”

Bar-Lev’s paternal grandparents were both in the Haganah — Moshe Bar-Lev was on death row at one point because the British police, for whom he worked, realized he was spying on them and stealing weapons — and they instilled in Amir this skepticism for the limits of tribalism.

“My grandfather was through and through a Jew,” the filmmaker recalls, “but he said to me, ‘We used to say in the movement [the Haganah], when the Messiah comes there’ll be no more Jews or non-Jews.’ Their Zionism was the antithesis of settler dogma.” (Amir’s grandmother, Rifka, taught Hebrew school in Berkeley for decades.)

Along with Bar-Lev’s grandparents, the Grateful Dead informed his distaste for turning idealistic principles into rigid beliefs and rules. Rather, his love of Judaism and the Dead derived from what they inspired in him, so he could make choices.

“I don’t like sitting and listening to a rabbi or engaging in celebrity adulation around the Grateful Dead,” he says. “What the rabbis, and the Grateful Dead, are hoping we get out of the thing is a kind of anti-authoritarian attitude. It’s not like they’re saying anything goes. It means you have to be the authority here. You have to figure out what’s right and wrong.”

Bar-Lev describes the band-fan relationship as “the Grateful Dead were meant to be the quarterbacks and all of us were going out for the pass.” That is, everyone had the space and the responsibility to express and extend the lessons of the Grateful Dead — experimentation, generosity, creativity, ethical behavior — in their own lives.

“Not every Jew necessarily buys into that,” Bar-Lev says, “but that’s what I got out of Judaism and that’s what I got out of Thomas Jefferson: You’re going to have to engage with the people you disagree with and engage with your own sense of right and wrong, and we’re going to quarrel our way into the future … together. I think that’s very Jewish on some level.”

“Long Strange Trip” screens at 2 p.m. Sunday, May 14 at the Sequoia Theatre in Mill Valley. The film opens May 25 at the Clay in S.F. and the Smith Rafael Film Center in San Rafael before premiering June 2 on Amazon Prime Video.