Some biographies set out to show that saints are merely men. The best biographies set out to show that saints are supremely men.

Surrounding last year's 200th anniversary of the abolition of the British slave trade, there was a spate of books, and a major film, focusing on the life of William Wilberforce, the figure most responsible for that massive moral achievement. Most of these efforts were inspiring but tended toward the worshipful. And worship -- as Lincoln biographies sometimes demonstrate -- can miniaturize a complex political accomplishment.

Now, slightly late but welcome nonetheless, William Hague -- the shadow foreign secretary of Britain's Conservative Party -- has produced a complete picture of Wilberforce and his times. Above all else, Wilberforce was a religious man. But "William Wilberforce: The Life of the Great Anti-Slave Trade Campaigner" is a political book, and gloriously so. As a major parliamentary figure, Hague is at home in the world of restive constituencies, unstable coalitions and sudden elections. As an accomplished historian, Hague also has an eye for the social context that shapes the largest of leaders.

Wilberforce was a paradox: A conservative in constant revolt against the social order of his time. Hague explains that revolt by vividly describing late-18th century corruptions. At the beginning of Wilberforce's career, elections involved the massive bribing of voters with ale, rum, wine and brandy. His first election cost the modern equivalent of 1 million pounds; no single British campaign in 2005 cost more than 14,000 pounds. Elections often included an undercurrent of violence, from dueling or the mob. Once in Parliament, members drank and gambled around the clock, with occasional breaks for public business. Most politicians were familiar with Mrs. Hazer's Establishment of Pleasure on Pall Mall.

In the midst of this fashionable decadence, a wealthy and witty young conservative politician experienced a profound spiritual crisis -- a "sense of my great sinfulness in having so long neglected the unspeakable mercies of my God and Saviour." Hague takes Wilberforce's religious conversion seriously, describing his consuming doubts, restlessness and agony -- and his resulting commitment to an evangelical Christianity that provided "the moral force and unshakeable will to become one of the greatest campaigners, and liberators, in the whole course of British history."

Young Prime Minister William Pitt, a close friend, also took Wilberforce's torments seriously, fearful he would lose a political ally to a life of "useless" religious contemplation. It was Pitt who urged Wilberforce to give his spiritual intensity a political outlet: ending the trade in human beings, on ships known as "part bedlam and part brothel."

Britain had been prepared for abolition by the philosophical objections to slavery of thinkers such as Adam Smith and the religious objections of preachers such as John Wesley. But justice is ultimately a political achievement. To pass the Slave Trade Act, Wilberforce and his allies invented the modern political pressure campaign, with its petitions and boycotts. In the process, they created a new form of politics -- human rights activism.

During his 45-year career, Wilberforce was attacked by social and economic radicals for refusing to support leveling equality for the British working class -- a charge which is true. "Wilberforce continued to believe," Hague comments, "that the real revolution that was required was in morals and education, so that people could become fit for the greater power they sought." This remains a conservative distinctive.

But Wilberforce was primarily attacked by conservatives who stood for tradition without moral vision. He was variously accused of undermining the British economy, gratifying "his humanity at the expense of the interests of his country," and proposing "romantic trials of compassion abroad."

All this has a modern resonance. Some conservatives still do not understand that a significant portion of their coalition, influenced by faith, hungers for trials of compassion, from the protection of innocent life to the fight against global disease, to the end of modern slavery.

Wilberforce spent 20 years of disappointment, tenacity and maneuver in his campaign against the slave trade before victory suddenly dawned in 1807. One contemporary concluded: "Hundreds and thousands will be animated by Mr. Wilberforce's example ... to attack all the forms of corruption and cruelty that scourge mankind."

Hague's life of Wilberforce should be read by every student of politics, to understand why mere prosperity and mere security will never be sufficient goals of evangelical political involvement. And this book should be read by every politician, to see what feats of honor are possible even in a very political life.