A portrait of Martin Luther at a museum in Potsdam, Germany. Luther sparked the Reformation 500 years ago this month. (Ralf Hirschberger/Picture-alliance/dpa/AP Images)

Andrew Pettegree is a professor of modern history at the University of St Andrews, Scotland, and the author of “Brand Luther: 1517, Printing, and the Making of the Reformation.”

When an emissary of Pope Leo X traveled to Germany in 1521, he found a land in turmoil. A young, inexperienced ruler, Emperor Charles V, struggled to assert his authority over a wily and unruly nobility. That, at least, was not unusual; what was new was the fact that all of this played out at the center of a media storm. The papal legate could hardly step out on the streets without being accosted by angry, agitated citizens. The name on everyone’s lips was that of an obscure Augustinian friar, Martin Luther. Four years earlier, Luther was an unknown professor at the new university in Wittenberg, a small town tucked away on Germany’s distant northeastern fringes. In 1517, Luther made a bold protest against the selling of indulgences, which offered penitent Christians the assurance of salvation in return for pious donations. To this point he had published virtually nothing. Yet by 1521, after a fury of controversial writing, Luther was the most-published author in the history of printing. When he died 25 years later, he would leave a church permanently and irrevocably divided, with consequences we still live with today.

This year’s 500th anniversary commemoration has unleashed a similar media storm, with a shoal of new studies of Luther and his movement. These two contrasting works make their own distinctive contributions.

Eric Metaxas is a renowned radio host and an experienced biographer, best known for his studies of William Wilberforce and Dietrich Bonhoeffer. In "Martin Luther: The Man Who Rediscovered God and Changed the World," he offers a meticulously researched and detailed account of Luther's life and times. This is not a self-consciously psychological study — indeed, he has some fun with historians who put Luther in the psychiatrist's chair — but it is nevertheless a very human portrait. Metaxas takes us through all the twists and turns of this almost impossibly dramatic life: the bold defiance of hierarchy, the gradual repudiation of the church that had made him. Then comes the confrontation with Charles V, the climactic end of the events that shaped Luther's journey to exclusion and outlaw.

Luther was now a man with a movement, which brought new responsibilities and challenges, not least the growing body of acolytes in Wittenberg. He had to cope with ominous signs of disorder as newly empowered citizens sought the authority of the Gospel in their hope for a better life — and, more parochially, the arrival in Wittenberg of a cartload of runaway nuns. One of these stowaways would become Luther’s wife. This ultimately happy union came in an impossibly challenging year, as Luther fended off criticism from Erasmus, dealt with the death of his protector Frederick the Wise and faced down a revolt that threatened to destroy his young movement. As peasant armies roamed the German countryside, claiming Luther’s Gospel message as their inspiration, portraits of the reformer in this year show Luther as a man on the verge of collapse. Yet he weathered the storm, decisively throwing in his lot with the state authorities. The course of the Reformation was set.

****HANDOUT IMAGE “Martin Luther,” by Eric Metaxas, (credit: Viking) ***NOT FOR RESALE (Viking )

Metaxas is a scrupulous chronicler with an eye for a good story. The result is full, instructive and pacey, but unusually discursive. When Luther makes his trip to Rome, we spend several pages with Pope Leo X and his elephant and, on the way home, a fraudulent holy woman. There is some florid phrase-making. Indulgences, apparently, “were like milkweed seeds borne aloft by the wind,” a description possibly more redolent in Iowa than in Manhattan; but then Iowa might have scratched its head at the “pre-Zapf dingbats” that apparently characterized the dispute between the theologian Prierias and Luther.

What does all this amount to? Metaxas is not unusual in seeing in Luther’s bold defiance of the papacy the birth of modern society. It is true that Luther was the first to harness the power of print to create a popular movement. The Reformation was, in its first manifestation, a media event, deploying a powerful new invention to speak over the heads of the clergy. It flattered the wider public by declaring their capacity to join the conversation. In his later years, when the fires of controversy dimmed, Luther was a visionary advocate of the power of education, insisting on schools for girls and boys as a means of creating an informed Christian public. But in other respects Luther was a profoundly conservative figure, deeply respectful of established social and gender hierarchies, impatient of dissent.

Brad Gregory is a very different sort of historian. Widely acknowledged as one of the most brilliant minds applied to the Reformation era, in recent years, Gregory has focused more directly on the consequences of these events, most notably in an ingeniously contrarian piece of polemical writing, "The Unintended Reformation: How a Religious Revolution Secularized Society." In his new book, "Rebel in the Ranks: Martin Luther, the Reformation, and the Conflicts That Continue to Shape Our World," Gregory takes us on a similar journey. Gregory is not a natural admirer, but this is a fair-minded and generous account of the evolution of Luther's theology. Gregory persuasively describes how the radicalism of Luther's ideas evolved out of the logic of events, especially the major confrontations with his critics at Augsburg and Leipzig. Gregory's tone is one more of sorrow than of anger, as he observes a talented son of the church who finds there is no place for him in an institution he saw as corrupt. In all of this, Gregory makes very good use of Luther's writings, offering a succinct precis of the major milestones of his developing thought. This brings out the radicalism of what Luther is about as he turns his fire on the pope, the cardinals and the sacramental order.

Gregory is less effective in explaining why, in very significant numbers, others were drawn to this tumultuous, unflinching, disturbing vision of the Christian life. Instead, he moves to more familiar ground, answering the rather easier question of why many who followed Luther in rejecting the papacy refused to be constrained by his vision of church order. In disavowing the authority of the pope, Luther offered no real guidance on where human responsibility for separating true from false interpretation should lie. His assertion that scripture alone should guide the Christian life was never much more than a debating ploy to avoid the embarrassing reality of his own role as the arbiter of true religion.

All of this Gregory lays out in painstaking detail, without revealing why he regarded this pluralism as inherently undesirable. Nor does he really answer the key question for critics of the Reformation: whether Western Christianity would have been better off had men like Luther swallowed their misgivings and toed the line. Gregory’s most fundamental charge is that Luther’s Reformation opened the door to the secularization of Western society. But Luther’s protest was in large part prompted by the very secular priorities of the late Medieval papacy, the ever-increasing monetization of salvation and the repeated use of excommunication as a tool to discipline secular rulers. It is worth asking how we got from Martin Luther to President Trump, but it is far from certain that an unchallenged imperial papacy would have left Europe much better off.

As German townsfolk followed the furor over Luther, what often caught their eye was the huge number of pamphlets pleading his cause, piled up on the bookstands in the market squares. It was not really what each of them said: The sheer numbers were a sort of surrogate for public opinion. The same might almost be said of the extraordinary outpouring of books on Luther this anniversary year. Metaxas credits Luther’s legacy as pluralism, religious liberty and personal responsibility; Gregory offers a lament for secularism. Big things for Luther’s admittedly broad shoulders to bear. But no one can doubt that this extraordinary, talented, restless, heedless man changed the direction of history.

Martin Luther

By Eric Metaxas

Viking. 480 pp. $30

Rebel in the Ranks

By Brad S. Gregory

HarperOne. 292 pp. $27.99