When else has the timing of a movie’s release ever been so bittersweetly correct? A lesson on how and why Martin Luther King Jr. compelled Lyndon Johnson to sign the Voting Rights Act of 1965, and inescapably an elucidation of not learning history and being doomed to repeat it, Selma has every right to slap us in the face with gloating didacticism. Instead, as reworked from Paul Webb’s script by director Ava DuVernay, it’s the picture of magnanimousness, an auspicious chronicle of human dignity. As Johnson, Tom Wilkinson proves unsentimentally reliable. As King, David Oyelowo proves astonishing. This is the great leader as we need to remember him — and also as a man, feeling sometimes tired and trapped, wearing history on his shoulders. Supporting players, particularly Carmen Ejogo as Coretta Scott King, also bloom with DuVernay’s respect. This is a film with resources — its producers include Oprah Winfrey, who also appears in a small but galvanizing role, and Brad Pitt — but DuVernay doesn’t allow it the luxury of going soft with good intentions. She simply stays the course of sharply intimate drama. Critique is possible: The slow-motion stylization of lethal violence, though consistently applied, steers sincerity toward triteness, and this true story might have been more affecting without it. But that’s a minor complaint. Ultimately, what makes DuVernay’s movie so good and necessary is that it actually lets us see the arc of the moral universe bending — being bent, by human will — toward justice.