In 1972, following a string of hits and Grammy awards, Aretha Franklin decided her next project would be a return to her roots. The daughter of a Detroit preacher, Franklin secured a Baptist church in Los Angeles for a two-night recording session, and the result was Amazing Grace, her most successful album and the top-selling gospel recording of all time.

Warner Bros Records hired Sydney Pollack to shoot the process, looking for a mix between a concert film and a making-of. Pollack had just directed They Shoot Horses, Don’t They? and had already wrapped production on Jeremiah Johnson. While this is hard to believe, the two-night production at the New Temple Missionary Baptist church resulted in useless footage. The crew neglected to slate the shots with clapperboards, necessary for synchronising sound and image – a mind-boggling omission and one reason why Amazing Grace is only making its debut in 2018.

After Pollack died in 2008, music producer Alan Elliot remedied the audio-visual issue using modern editing tools. The film was set to be screened at the Telluride and Toronto film festivals in 2015, but a last-minute injunction by Franklin herself stopped it: her reasons remain a mystery. Now, however, three months after her death, the movie is ready for its one-week qualifying run for an Academy award.

Franklin feels the heat under the film crew’s lights. Photograph: courtesy of Al’s Records and Tapes

Clearly there are ethical questions about watching a film that the subject didn’t want you to see. And we can quibble as to whether Pollack, Elliot or credited editor Jeff Buchanan is the true author of the piece. But this is all secondary to the fact that Amazing Grace is, without a doubt, one of the finest music documentaries ever. For close to 90 minutes I sat with chills up and down my spine in a near-constant roll. Franklin singing gospel in a badly lit church with rows of cheap movie theatre seats filled with ecstatic fans is a balm for the spirit, and something that needs to be seen.

The film is almost wall-to-wall music, with Franklin barely acknowledging the audience between songs. The musical director is the affable Rev James Cleveland, who also sings and plays piano. The Southern California Community Choir, decked out in shiny silver vests, is led by its enthusiastic conductor the Rev Alexander Hamilton. The remainder of the group include top session men, such as Bernard “Pretty” Purdie on drums and Chuck Rainey on bass. But this isn’t a studio, it’s a church loaded with sound gear and a team of cameramen buzzing around. Cleveland at one point offers up an “amen” to the cessation of technical difficulties.

It’s unclear to what extent Pollack dressed the set. A huge painting of a rather muscular Christ emerging from his baptism hangs behind the choir; to the side there’s an American flag. Everyone is sweating under the hot lights, especially Aretha who stands not under a spotlight, but behind a pulpit: she isn’t performing, she is testifying.

The song selection is a mix of traditional gospel tunes plus a little Marvin Gaye and Carole King. At the halfway mark comes an astounding rendition of Amazing Grace that is stretched out to nearly 11 minutes. The camera moves across the faces of the choir, who are first to leap to their feet in support. Then the audience, then Cleveland, who moves from teary to full-on sobbing. By the end of the song the entire church is a mess, but somehow Aretha keeps it together and hits each note perfectly.

Franklin lets Cleveland do the talking for her on night one, but on night two there’s a visit from her father, who doesn’t just give a touching speech, he comes up to mop her brow when the sweat gets too much.

Also in the crowd on night two are Mick Jagger and Charlie Watts, who were in Los Angeles finishing the Stones’ career highlight Exile on Main St, and there is no doubt that the gospel inflections of songs such as Shine a Light and Let It Loose were inspired by this visit.

Four decades on, Amazing Grace offers an abundance of time-capsule treasures – the clothing, the dancing, the very visible camera gear. Pollack skitters around, pointing at members of the crowd with a “shoot that” urgency to members of his camera crew. There are also noticeable racial inequalities that wouldn’t be quite as stark today. The entire crew is white, the audience almost entirely black. The vibe of the film exudes positivity, but there is an inevitable optic of ethnography with a setup like that.