John Ford’s “The Grapes of Wrath” is a left-wing parable, directed by a right-wing American director, about how a sharecropper’s son, a barroom brawler, is converted into a union organizer. The message is boldly displayed, but told with characters of such sympathy and images of such beauty that audiences leave the theater feeling more pity than anger or resolve. It’s a message movie, but not a recruiting poster.

The ideological journey of the hero, Tom Joad, can be seen by the two killings he is responsible for. The first one takes place in a saloon before the action begins, and Tom describes it to a former preacher: “We was drunk. He got a knife in me and I laid him out with a shovel. Knocked his head plum to squash.” After serving four years, Tom is paroled and returns to his family farm in Oklahoma, only to learn the Joads have been “tractored off the land” and are joining the desperate migration to California. Near the end of the film, after seeing deputies and thugs beat and shoot at strikers, he is once again attacked, this time by a “tin badge” with a club. He snatches away the club, and kills him. The lesson is clear: Tom has learned who his real enemies are, and is working now with more deserving targets.

The movie was based on John Steinbeck’s novel, arguably the most effective social document of the 1930s, and it was directed by a filmmaker who had done more than any other to document the Westward movement of American settlement. John Ford was the director of “The Iron Horse” (1924), about the dream of a railroad to the West, and made many other films about the white migration into Indian lands, including his Cavalry trilogy (“Fort Apache,” “She Wore a Yellow Ribbon,” “Rio Grande”). “The Grapes of Wrath” tells the sad end of the dream. The small shareholders who staked their claims 50 years earlier are forced off their land by bankers and big landholders. “Who’s the Shawnee Land and Cattle Company?” asks Muley, a neighbor of the Joads who refuses to sell. “It ain’t anybody,” says a land agent. “It’s a company.”

The movie finds a larger socialist lesson in this, when Tom tells Ma: “One guy with a million acres and a hundred thousand farmers starvin’.” Of course Tom didn’t know the end of the story, about how the Okies would go to work in war industries and their children would prosper more in California than they would have in Oklahoma, and their grandchildren would star in Beach Boys songs. It is easy to forget that for many, “The Grapes of Wrath” had a happy, unwritten, fourth act.

When Steinbeck published his novel in 1939, it was acclaimed as a masterpiece, won the Pulitzer Prize, was snatched up by Darryl F. Zanuck of 20th Century-Fox and assigned to his top director, John Ford. It expressed the nation’s rage about the Depression in poetic, Biblical terms, and its dialogue does a delicate little dance around words like “agitators” and “Reds”–who are, we are intended to understand, what the fat cats call anyone who stands up for the little man. With Hitler rising in Europe, Communism would enjoy a brief respite from the American demonology.

The movie won Oscars for best director and best actress (Jane Darwell as Ma Joad) and was nominated for five others, including best actor (Henry Fonda) and best picture (it lost to Hitchcock’s “Rebecca”). In a year when there were 10 best film nominees Ford had even another entry, “The Long Voyage Home.” “The Grapes of Wrath” was often named the greatest American film, until it was dethroned by the re-release of “Citizen Kane” in 1958, and in the recent American Film Institute poll it finished in the top 10. But do many people watch it anymore?

Viewers will discover a film that uses realistic black-and-white cinematography to temper its sentiment and provide a documentary quality to scenes like the entry into the Okie transient camp near the California border. Even though the Joad farm is a studio set, Ford liked to shoot on location, and records a journey down Route 66 from the Dust Bowl through New Mexico and Arizona, past shabby gas stations and roadside diners. The dialogue sometimes grows a little too preachy to fit within the simple vernacular of farmers, and Tom Joad’s famous farewell to Ma (“Wherever there’s a fight so hungry people can eat, I’ll be there. Wherever there’s a cop beatin’ up a guy, I’ll be there …”) always sounds to me like writing, not spontaneous expression.

But it is dialogue spoken by Henry Fonda, whose Tom Joad is one of the great American movie characters, so pure and simple and simplytherein the role that he puts it over. Fonda was an actor with the rare ability to exist on the screen without seeming to reach or try, and he makes it clear even in his silences how he has been pondering Preacher’s conversion from religion to union politics. We’re not surprised when he tells Ma, “Maybe it’s like Casy says. A fella ain’t got a soul of his own, just a little piece of a big soul. The one big soul that belongs to everybody.” Just as, in the dream of One Big Union, transcendentalism meets Marxism.

The power of Ford (1884-1973) was rooted in strong stories, classical technique and direct expression. Years of apprenticeship in low-budget silent films, many of them quickies shot on location, had steeled him against unnecessary set-ups and fancy camera work. There is a rigorous purity in his visual style that serves the subject well. “The Grapes of Wrath” contains not a single shot that seems careless or routine.

“The Grapes of Wrath” shows half a nation with the economic rug pulled out from under it. The story, which seems to be about the resiliency and courage of “the people,” is built on a foundation of fear: Fear of losing jobs, land, self-respect. To those who had felt that fear, who had gone hungry or been homeless, it would never become dated.