Whenever liberals are in a mood to warn Americans about the frightful threat of conservative Christianity, they round up the usual suspects: Jerry Falwell, Pat Robertson, or perhaps some wild-eyed sniper at an abortion clinic. One name they never bring up is Charles Colson.

No wonder. The celebrated born-again Christian--a former Nixon tough guy who did prison time for his part in Watergate--has spent three decades ministering to inmates and their families. It might easily have never happened: Colson's conversion story almost lured him into the burgeoning subculture of celebrity Christianity. Instead, he founded Prison Fellowship and plunged into the world of barbed wire, watchtowers, and cell blocks.

Along the way, Colson has become one of the most influential evangelicals of his generation, especially in the era of the Bush White House. Yet he's never forgotten his experience behind bars, as anyone who has traveled with him into prisons can attest. Here is an evangelist to the core, a thoroughly converted man. "By anybody's certification, it stuck," religious historian Martin Marty once said of him. "It is very deep, very profound, very tested."

In Charles W. Colson: A Life Redeemed, Jonathan Aitken offers a character sketch of Colson's journey to the pinnacle of power, then disgrace, vilification--and restoration. It's a task for which Aitken is uniquely suited. A former member of parliament whose perjury conviction ended his own political career, he himself has converted to Christianity, making big news inside and outside of church circles. This allows Aitken to trace Colson's spiritual trek with care, though at times it may make his writing a little opaque to the uninitiated.

Aitken devotes about half the book to the years before Colson's crisis of faith. He reveals, for example, the young Boston lawyer who scorns the establishment by hiring an African American as his partner. Yet there's also Colson the Republican ideologue who orchestrated smear campaigns against Democratic opponents. By the time he arrived as special adviser in the Nixon White House, he was as enamored with the promise of politics--what Hillary Clinton once called the "politics of meaning"--as anyone could be.

Then came the crash. At the height of the Watergate scandal, Colson turned to an old friend for counsel, Raytheon president Tom Phillips. What he heard, instead, was the religious equivalent of a habeas corpus: a riveting and incriminating description of the sin of pride, drawn from the pages of C.S. Lewis's Mere Christianity. As Aitken tells it, Nixon's "hatchet man" needed more than an emotional appeal to repent and believe, and Lewis--the premier Christian apologist of the 20th century--gave it to him. Since then, Colson has written or coauthored 23 books on topics ranging from crime to Christian theology. Few evangelical leaders have spent as much time arguing that the intellectual life be cultivated for the glory of God.

Aitken's treatment of Colson the social reformer forms the heart of the book. It is thorough and fair-minded, though not as richly drawn as it might be. Aitken only begins to suggest the profound conceptual challenges that Colson's ministry presents to both left and right.

For decades now, leaders of the religious left, from Jesse Jackson to Jim Wallis, have raised their self-described "prophetic voice" on behalf of the poor. What that voice usually demands is more government spending for secular social services. So they create ad campaigns, assemble political action groups, and get themselves arrested at rallies in Lafayette Park. Not Colson. He just keeps inventing new ways for churches to help inmates and their families recover from the blight of crime.

Church-based voluntarism is the key. Founded in 1976, Prison Fellowship now offers religious and educational programs to inmates in over 800 prisons in 40 countries. The Angel Tree Ministry, a staple of local churches across denominational lines, delivers 600,000 gifts each year to the children of prisoners. Colson's program for ex-offenders, which pairs volunteers with former inmates to help them find jobs and housing, has gotten support from the Bush White House. There's even a program for the victims of crime. All counted, Prison Fellowship sustains a $50 million budget, with over 300 staff and nearly 24,000 volunteers, virtually all privately supported.

Colson's theology presents a more fundamental challenge to liberalism. All of his work among criminals is anchored in the core doctrines of evangelical Christianity. The taproot of crime, he says, is sin--not economic injustice. Thus, "rehabilitation" depends, ultimately, on personal repentance and faith in Jesus. Aitken, who followed Colson into several prisons, effectively describes how he establishes rapport with inmates and brings a message of hope and redemption, even to those on death row.

"You and I know about tombs, because prisons are the tombs of our society and we're in one now," he tells Texas inmates at an Easter Sunday service. "But you and I also know that the only way to come out of these hellholes, these tombs, is by knowing the risen Lord."

If Colson's initiatives upset the secular assumptions of the left, he also unsettles the political and religious right. Consider, again, the issue of crime. Conservatives may be more likely than liberals to talk about sin, but they also love incarcerating sinners. The problem with that, Colson says, is that most prisoners will be released--but probably unprepared for life on the outside. So he's elevated the concept of "restorative justice," the idea that offenders must be held accountable to their victims, make restitution, and even be reconciled when possible. This is how Prison Fellowship turns convicts into citizens.

Or take the issue of the culture wars. Colson is one of the few evangelical leaders willing to chide his brethren for their all-or-nothing approach to politics: They either behave as if politics can usher in the kingdom of heaven or withdraw from politics altogether. Aitken gives due attention to a long and serious interest in cultural renewal. Colson's conclusion: It won't happen until Christians think responsibly about how their beliefs should shape the contours of modern life--intellectually, socially, and politically. It's not a message, however, that makes for flashy fundraising letters.

One story Aitken recounts captures Colson's sanctified grit. He was in Georgetown University Hospital, recovering from a painful stomach tumor. He learned that, in a room just above him, was former CIA Director William Casey, a friend since his days with Nixon. Casey was on his deathbed. Colson, with his intravenous drip in hand, got cleared by CIA guards and slipped into his room. Casey couldn't utter a word. But Colson took his hand, spoke with him about Jesus, and prayed with him to receive Christ as his savior. It was, he said later, "the real reason I was in that hospital."

Herein lies much of Colson's appeal. It's not just his track record of translating his beliefs about God into visible acts of mercy. For Colson, Christian faith must be informed by reason, conscience, empathy, and experience. The English poet Thomas Traherne once remarked that "he who thinks well serves God in his inmost court." It's an insight that many Christians arguably ignore. Chuck Colson learned it early in his walk of faith, and thousands would consider themselves blessed by his discovery.

Mr. Loconte is a research fellow in religion at the Heritage Foundation and editor of "The End of Illusions: Religious Leaders Confront Hitler's Gathering Storm" (Rowman & Littlefield). He served as a member of the Congressional Task Force on the United Nations.