The Martin Luther King Jr biopic Selma is primarily composed of individuals undergoing impassioned debates. We watch King (David Oyelowo) and Lyndon B Johnson (Tom Wilkinson) verbally spar over voting rights; with segregation outlawed in 1960s America, African-Americans find their legal right to vote denied, and divided camps of activists argue about the best way to achieve change – and the type of change that’s required.

Having arrived in Selma, Alabama with the express purpose of realising such change, King cuts through a town hall debate with local campaigners SNCC (the Student Nonviolent Co-ordinating Committee). SNCC’s grassroots work, he argues, is admirable but comparatively ineffective because it focuses on black awareness. As his voice assuming that trademark fiery fervour – impressively imitated by Oyelowo – he outlines his agenda: to attract cameras, to attract controversy and, most of all, to attract white awareness.

It’s fair to say that Selma’s director, Ava DuVernay, has similar objectives. Not that her film is directed specifically towards white audiences, but that her approach to telling this important story hews closer to the inclusive activism of Dr King than, say, the militant approach of his contemporary Malcolm X (who makes a brief appearance in the film, played by Nigel Thatch, in another debate about activism with Coretta King (Carmen Ejogo)). DuVernay takes the biopic formula and weaponises it, preserving its conventions but carefully calibrating them to accommodate a story that’s true to MLK’s essence as it pulses with modern resonance.

Those conventions do tend to sap the film of some of its vitality. The opening half hour of the film is burdened by the need to – much like an effective speech – ensure the facts and stakes are clearly outlaid. There are effective scenes here: Martin and Coretta waxing rhapsodic about a quiet life they’ll never have before he accepts the Nobel Peace Prize, or an expressionistic explosion tearing through a church – a beautiful tragedy. But then there are scenes where LBJ awkwardly addresses the head of the FBI as “J. Edgar” to catch-up the slower audience members and we’re reminded of the sort of film we’re watching. These issues evaporate as the film progresses, and are arguably necessary concessions to make to ensure the film appeals to a wider audience – including Oscar voters, who grudgingly nominated the film for Best Picture and Best Song.

DuVernay deserved to be in the Best Director line-up. The proof is the pudding – well, the middle of the pudding, as the film picks up some steam in the second act. Moments of awkward exposition are forgiven when we survey the horror of the murder of Jimmie Lee Jackson (Keith Stanfield, who after Short Term 12 is proving himself to be one of the most exciting – and under-used – young actors around) at the hands of vengeful white police officers, in a moment that captures the horrific impotence evoked by the recent deaths of Michael Brown or Eric Garner. Or the astounding, breathtaking setpiece of the first attempt at a march from Selma to Montgomery, met with vicious violence in a dense fog of tear gas and hatred.

Oyelow delivers a better performance than any of the five men nominated for Best Actor this year, while we’re at it. It’s a tricky task for an actor to portray a man like MLK. The word “hagiography” gets bandied around a lot when it comes to films about great men like this, meaning the biography of a saint. Selma doesn’t exactly canonize King – he’s a man as well as a myth, prone to personal weakness and infidelities – but it doesn’t shy away from depicting him as a saint. DuVernay consistently places him at the centre of the frame; he’s often imbued with a heavenly light or granted a halo by the coronas of reflected light that encircle him. The film respects the integrity of the man too much to entirely perforate his superhuman aura. This might be regarded as a failure if Selma were a character study of King, but that’s not what it’s trying to achieve.

Perhaps I misspoke describing Selma as a biopic before. While King is undeniably the centre of the film and the film follows many of the tropes of Hollywood biographical features, this is not simply a portrait of one man achieving greatness. Rather, it’s an inclusive story, including within its sweep President Johnson, close-minded governor George Wallace (Tim Roth), SNCC leader John Lewis (Stephan James) and many others. It operates almost like a history lesson – and will, no doubt, be shown in history classes for decades to come.

This somewhat explains the vocal minority of naysayers protesting the film’s depiction of LBJ. Because Selma frames itself as an objective historical retelling and places a black man – not a white man – at its centre, those looking to preserve a white-centric model of history become anxious. I suspect they’re less concerned about an unflattering portrait of LBJ (who I felt came across as a decent if conflicted man) than a portrait of LBJ that reveals the strength of King’s influence. Late in the film, Johnson rejects Wallace’s racism in a confrontation in the Oval Office, and he finds himself repeating King’s words to the racist governor, realising the importance of his historical legacy. I imagine this scene stung for those with a white-centric view of history, where changes are made only by powerful white men. Selma rejects the white saviour – and the argument that King’s protests were ‘ordered’ by LBJ – for a different perspective on history.

Selma’s conventional approach ensures its own historical legacy; it will be remembered long after films like American Sniper and The Imitation Game have faded from the public consciousness, whether or not it wins any Oscars come February 22^nd. It will find its way into classrooms in part because of its approachable biopic format, but it will resonate because of how it channels the sense of hopelessness and rage watching Jimmy Lee Jackson die, or the hair-raising power of watching Oyelowo embody King in his climactic speech on the steps of the Montgomery courthouse.