LOOKING AROUND THEM, AMERICANS see a relentlessly individualistic brand of Christianity. Members of informal Protestant sects in growing exurbs shop for their megachurch of choice to listen to preachers often certified by mail. And many Christians belonging to mainstream churches adopt the doctrines they agree with and ignore the rest. And yet, if one asks Americans about the history of American religion, they will probably point to the Puritans and the Pilgrims or other churches strict in their doctrine and intolerant of deviance. Some may think of Jonathan Edwards, the preacher of "Sinners in the Hands of an Angry God." In short, Americans seem to think that their current freemarket approach to religion arose contrary to a tradition of rigorous orthodoxy.

The sketch above is a caricature, of course. But it reveals a deep misconception that does, in fact, seem to lie at the heart of the way Americans understand their religion. This is the assumption that American individualism radicalized American religion sometime after the country had been established. But, in truth, a rather different development occurred: American Protestantism, in its radical individualism, indelibly molded our culture even as it became secular. At the beginning of the forgotten history that prompts this interpretation is an obscure figure who died 300 years ago this year. His name was Philip Jakob Spener (1635-1705).

Spener was an earnest and devout Lutheran, beginning his career as a minister in Frankfurt in 1666. Born near the end of the Thirty Years' war, and after a century of intermittent religious strife, Spener lived in an age weary of conflict but still yearning for transcendence. Although all Europeans were required to belong to one of the three denominations on the Continent (Roman Catholicism, Lutheranism, and Calvinism), Spener detected that many lacked the genuine inner faith he considered essential to true Christianity. Although a dutiful adherent of orthodox Lutheran theology, Spener valued it primarily insofar as it furthered the practice of piety among Christians. He declared, in his controversial tractate Pia Desideria, that intellectual approaches to faith from a distant clergy left the laity indifferent to religion--or, worse, Christians in name only. An account of the inadequacies of the Lutheran church in his day, Pia Desideria offered six proposals to renew the internal faith of believers, to bring about in them spiritual rebirth. For Spener, a mystical experience of faith, rather than the theological knowledge of it, sowed the seed of true Christianity.

Thus, at the center of all Spener's proposals was a conception of Christianity that still prevails in much of America today: a religion, essentially, of the heart. "Our whole Christian religion consists of the inner man or the new man, whose soul is faith and whose expressions are the fruits of life," he declared. He then defined that inner man: "We lay the right foundation in the heart," and his proposals made changing the heart of the believer so that he might live according to the Gospel the foremost function of the church and its priesthood. He recommended that clergy be educated to preach the Bible effectively to the laity, and that the laity take a role in the ministry of the church. His most famous recommendation was to institute collegia pietatis, groups of the devout that came together to read and discuss the Bible. In other words, Bible study. Spener pushed Luther's Reformation further than did Luther himself, insisting on the personal, emotional experience that the believer has of the Holy Spirit, especially through the Gospel: "We must let it penetrate to our heart," he wrote, "so that we may hear the Holy Spirit speak there, that is, with vibrant emotion and comfort feel the sealing of the Spirit."

So what do the thoughts of a German Lutheran in the 17th century have to do with American religion? It is a circuitous, but vital, connection. Well before Spener published Pia Desideria in 1675, he was holding collegia pietatis in his own home and gathering followers, who eventually became known as Pietists. Europe was teeming with Christian sects preaching a mystical spiritualism. Spener provided a basic intellectual framework for this subjective spiritualism, grounding it in a heartfelt experience of the Word and total fidelity to Scripture. With the approval of the sympathetic Prince Frederick III (later King Frederick I of Prussia), Spener staffed the newly-founded University of Halle in Saxony with Pietist theologians.

Under the direction of Spener's student and collaborator, August Hermann Franke, Halle became the cradle of an increasingly international Pietist movement, one that trained missionaries and ministers and then dispatched them all over the world, including America. One of Franke's early students, and Spener's godson, was the eccentric (and wonderfully named) Count Nicholas Ludwig von Zinzendorf, a believer in what he called "heart religion." When a group of Pietistic Moravian exiles sought refuge on the Count's estate, Zinzendorf soon became the leader of the community, which called itself the Moravian Brethren. Moravian Brethren became a major missionary force, emigrating to Africa, Russia, Holland, England, and America.

While on a ship to Georgia in 1736, they began in a young John Wesley his own spiritual renewal. Two years later, Wesley underwent his definitive conversion experience and went to study at Halle. When he came back, he initiated his Methodist movement in England, and many of his missionaries ended up in America, where Methodism today ranks as the second largest Protestant denomination.

Spener himself was a quiet, irenic Lutheran minister, but the ideas he unleashed soon led many well outside the orthodox Lutheran fold. His emphasis on a priesthood of all believers (something Luther had taught), and his assertion of the essential value of the subjective experience of the Spirit, led many to dismiss theology and the church hierarchy altogether. He fanned the embers of the Reformation of the 16th century and set new fires of his own, which soon enflamed radical pietists all over Germany. Persecuted by the various German governments, many of these priests, too, ended up in America, settling in Pennsylvania, New Jersey, New York, and elsewhere. Pietism flowed through several channels to American shores, carrying Spener's fundamental ideas through mainstream Protestant churches and more radical Pietistic movements.

In a sense, American Christianity is constantly experiencing the Reformation. From the Puritans and the Dutch Reformed to the Pietists and the Methodists, the most individualistic and radical sects of Protestantism all came to America, and continued to preach the ideas that had brought them there. Indeed, as many sects have emerged in America, within and without the mainstream denominations, as came here fully formed. The Pietist presence is just one part of this constant proliferation, but it is a part worth remembering, for its essential ideas run through much of American Protestantism. Jonathan Edwards, the great preacher of the Great Awakening, borrowed much from the Pietists and Methodists, whom he knew and whose writing he read. Even Catholics in America often show Pietistic leanings, insisting on the validity of their own emotional experience and interpretation of faith over instruction from the Vatican.

Spener articulated the central ideas that shape not only American religion, but the American personality. For Spener and the generation of evangelists he inspired, three principal concerns seemed to crowd out most others. The first was that the people of the church--the laity--should have a voice with the appointed caretakers--the priests--in its direction. The second, which Spener initiated and Franke furthered, was the importance of the emotional experience of the faith--in particular, of a conversion as the pivotal experience of a Christian's life. Finally, the practice of Christianity superseded knowledge of its dogma. These seem typical of American attitudes: a resistance to a hierarchy that claims moral authority, a sentimental religiosity that tests convictions primarily by personal experience, and an emphasis on living a Christian (or perhaps merely virtuous) life according to how one feels rather than what one thinks.

American Christianity is famously inventive and free-wheeling. And while it might seem self-evident to do so, commentators seldom explain the state of American religion as a product of religious history. Some may explain it as a consequence of a country that values free choice, or as the fruit of competition among religious denominations. But America's religious history leads quite naturally to its religious present. The populist, sentimental, and individualistic character of American religion is a continuation on this continent of the protest movement that began nearly 500 years ago in Europe. Any church on this soil, especially any church established on pietistic premises, faces the essential standard of faith described by Philip Jakob Spener: "We must let it penetrate to our heart, so that we may hear the Holy Spirit speak there; that is, with vibrant emotion and comfort feel the sealing of the Spirit."

Daniel Sullivan is a writer in New Jersey.