By JOSEPH LOCONTE

In April 1933, during the early months of Nazi rule in Germany, the “Aryan Paragraph,” as it came to be called, went into effect. A new law banned anyone of Jewish descent from government employment. Hitler’s assault on the Jews—already so evidently under way in his toxic rhetoric and in the ideological imperatives of his party—was moving into a crushing legal phase. German churches, which relied on state support, now faced a choice: preserve their subsidies by dismissing their pastors and employees with Jewish blood—or resist. Most Protestant and Catholic leaders fell into line, visibly currying favor with the regime or quietly complying with its edict.

Such ready capitulation makes the views of Dietrich Bonhoeffer, a young Lutheran theologian in Hitler’s Germany, all the more remarkable. Within days of the new law’s promulgation, the 27-year-old pastor published an essay titled “The Church and the Jewish Question,” in which he challenged the legitimacy of a regime that contravened the tenets of Christianity. The churches of Germany, he wrote, shared “an unconditional obligation” to help the victims of an unjust state “even if they [the victims] do not belong to the Christian community.” He went further: Christians might be called upon not only to “bandage the victims under the wheel” of oppression but “to put a spoke in the wheel itself.” Before the decade was out, Bonhoeffer would join a conspiracy to assassinate Hitler and pay for such action with his life.

In “Bonhoeffer: Pastor, Martyr, Prophet, Spy,” Eric Metaxas tells Bonhoeffer’s story with passion and theological sophistication, often challenging revisionist accounts that make Bonhoeffer out to be a “humanist” or ethicist for whom religious doctrine was easily disposable. In “Bonhoeffer” we meet a complex, provocative figure: an orthodox Christian who, at a grave historical moment, rejected what he called “cheap grace”—belief without bold and sacrificial action.

Since the 1960s, some of Bonhoeffer’s admirers have seized upon a phrase from one of his letters—”religionless Christianity”—to argue that he favored social action over theology. In fact, Bonhoeffer used the phrase to suggest the kind of ritualistic and over-intellectualized faith that had failed to prevent the rise of Hitler. It was precisely religionless Christianity that he worried about. After a 1939 visit to New York’s Riverside Church, a citadel of social-gospel liberalism, he wrote that he was stunned by the “self-indulgent” and “idolatrous religion” that he saw there. “I have no doubt at all that one day the storm will blow with full force on this religious hand-out,” he wrote, “if God himself is still anywhere on the scene.”

As the storms of hatred raged in Germany, Bonhoeffer moved beyond “confession”—that is, preaching and writing—and into rebellion. By the summer of 1940, he was recruited by Adm. Wilhelm Canaris and others as a double agent for their conspiracy against Hitler, an effort that operated out of the Abwehr (Nazi military intelligence). Henceforth he would pretend allegiance to the regime and pass along to the conspirators—whose goal was Hitler’s assassination—whatever intelligence he could gather. He depended on deception for his survival.

It was a bizarre role for a religious man, and a hitherto loyal German citizen, to play. As Mr. Metaxas notes: “For a pastor to be involved in a plot whose linchpin was the assassination of the head of state during a time of war, when brothers and sons and fathers were giving their lives for their country, was unthinkable.” And yet it became thinkable for Bonhoeffer precisely because his understanding of faith required more than adhering to tidy legalisms about truth-telling and nonviolence.

Mr. Metaxas notes that Bonhoeffer drew deeply from historic Christianity, especially its emphasis on the love of God expressed in the life and teachings of Jesus. Bonhoeffer also had an extraordinary capacity for empathy, responding with ever more horror to the plight of those around him. In his book “Ethics” (1949), he chastised those who imagined they could confine their faith to the sanctuary and still live responsibly in an unjust world. In “The Cost of Discipleship” (1937), he made unreserved obedience to Jesus—in every realm of life—the mark of authentic belief. “If we worry about the dangers that beset us, if we gaze at the road instead of at him who goes before, we are already straying from the path.”

It is here that many who invoke Bonhoeffer for their own causes stumble grievously. Atheists such as Christopher Hitchens praise his “admirable but nebulous humanism.” Liberals exalt his social conscience while setting aside his belief in sin and judgment. The theologian Stanley Hauerwas has even tried to recruit Bonhoeffer for the pacifist cause. But Bonhoeffer argued pointedly in the opposite direction. “Only at the cost of self-deception,” he wrote, can observant Christians preserve a facade of “private blamelessness clean from the stains of responsible action in the world.”

After a failed assassination attempt on Hitler in 1943, Bonhoeffer was arrested on charges of assisting Jews and subverting Nazi policies. Two years later, in early April 1945—after his full involvement in the conspiracy became known—he was executed at the Flossenburg concentration camp in Bavaria. By all accounts he faced with courage and serenity the ultimate consequence of his choices. His was a radical obedience to God, a frame of mind widely viewed today with fear and loathing, even among the faithful. In “Bonhoeffer,” Mr. Metaxas reminds us that there are forms of religion—respectable, domesticated, timid—that may end up doing the devil’s work for him.

Mr. Loconte is a senior lecturer in politics at the King’s College in New York City and the editor of “The End of Illusions: Religious Leaders Confront Hitler’s Gathering Storm.”

(wsj.com)