For all its good intent, excellent cast and glossy production, Amazing Grace is destined to play in more classrooms than theatres. A biopic of British abolitionist William Wilberforce focusing on his two-decade crusade to end the slave trade, the film is earnest and talky despite efforts to incorporate romance and humor. Social reformers aren't action heroes, of course, and our protagonist is refreshingly life-size--a gifted orator and tenacious organizer who suffered from colitis and chronic shyness--but this Wilberforce exudes as much charisma as Ralph Nader. "To most people at the time, the idea of abolishing the slave trade was ludicrous," director Michael Apted has said, offering an apt simile, "like someone today suggesting that we abandon the internal combustion engine."

Wilberforce, the son of a wealthy merchant, was fresh out of Cambridge when he was elected to Parliament in 1780. Five years later, he experienced a religious conversion and embraced the abolition movement, an unpopular cause in a country with an economy tied to the slave trade. A small but determined band of evangelicals nevertheless mounted a campaign to educate the public about the evils of the institution, led by minister John Newton, financier Henry Thornton, and indefatigable activist Thomas Clarkson. Wilberforce became their spokesman in Westminster.

Apted, who's made notable documentaries (the 7 Up series) as well as acclaimed features (Coal Miner's Daughter, Gorillas in the Mist, The World Is Not Enough), opted to emphasize the efficacy of politics over prayer, recognizing the abolitionists' faith but dramatizing their political acumen and social conscience. One might say the film sermonizes, but these progressive zealots, or rather, zealous progressives, are motivated by righteous indignation instead of moral righteousness. Indeed, Wilberforce makes a better pantheist than he does a Christian, and the penitent Newton, a former slave-ship captain given to wearing sackcloth, seems more at home in the House of Commons than the house of God.

On the other hand, Clarkson really was a prototype for the modern political operative, tirelessly gathering evidence, writing tracts and agitating for his cause. Apted and screenwriter Steven Knight (Dirty Pretty Things) pointedly avoid graphic representation of slavery and violence--an approach to history that would perplex Mel Gibson--so they don't depict the near-fatal beating Clarkson received from thugs hired by vested interests to shut him up. But this is Wilberforce's story, anyway. The film's dramatic tension must hinge on whether his health will hold for another year of debate...on whether he will find a wife to help him maintain his delicate constitution.

Ioan Gruffudd, who looks a bit like Nader, stars as the unfortunately named Wilberforce. (How does one not think of The Ladykillers?) Albert Finney plays Newton, who wrote the hymn "Amazing Grace" and, in an instance of genuine irony, went blind at the end of his life, after devoting his later years to cleansing his soul. Rufus Sewell makes an appealing Clarkson, a man yearning to act rather than argue.

The film benefits from wry performances by Michael Gambon as Lord Fox, liberal pioneer of political sarcasm; Toby Jones as the Duke of Clarence, dissipated son of King George III and poster boy for bigots-in-wigs; and Benedict Cumberbatch as William Pitt the Younger, appropriately the youngest prime minister in British history. Romola Garai is Barbara Spooner, Wilberforce's thoroughly modern life partner, and Nicholas Farrell is Henry Thornton, Wilberforce's best buddy and founding member of the Chatham Sect, a group of evangelicals who, were they alive today, would probably be ardent supporters of George Bush. Senegalese pop star Youssou N'Dour makes a superb film debut as Oloudah Equiano, the African slave who bought his freedom, settled in London and wrote a much-read book about his remarkable life.

Apted seems to draw a parallel between the British predicament at the end of the 18th century and the American one at the beginning of the 21st--one interesting scene features a legless veteran of the colonial wars begging for alms. Or perhaps it's Apted's interpretation of Regency London that begs for contemporary comparison. One thing for certain: Amazing Grace gives that old-time religion a shiny new look.