For a thousand years, a period that began with what some historians called the “Dark Ages” in the Christian West and that endured through both the Eastern and Western extensions of the Roman Empire, the essence of Christian faith was guarded differently than it had been in the first three centuries, before Christianity became official; throughout the Middle Ages itself the understanding of the essence evolved. In the 4th and 5th centuries, theologians including St. Ambrose, St. Augustine of Hippo, and St. Jerome laid the foundations for the development of Christian thought. By the 5th century, the bishop of Rome, the pope, as a result of conciliar decisions and unique events in Rome, had become the leading spokesman for the faith in Latin, or Western, Christendom. This position would assume greater institutional strength in later periods of the Middle Ages. In the Eastern churches, despite the claims of the patriarch of Constantinople, no single pontiff ruled over the bishops, but they saw themselves just as surely and energetically in command of the doctrines that made up the essence of Christianity.

The Western drama, especially after the year 1000, was more fateful for Christianity in the modern world. The pope and the bishops of Latin Christendom progressively determined the essence through doctrines and canons that enhanced the ancient grasp of faith. As they came to dominate in Europe, they sought to suppress contrary understandings of the essence of the faith. In the 14th and 15th centuries, Jews were confined to ghettos, segregated and self-segregated enclaves where they did not and could not share the full prerogatives of Christendom. When sects were defined as heretical—Waldenses, Cathari, and others—because of their repudiation of Roman Catholic concepts of Christian essence, they had to go into hiding or were pushed into enclaves beyond the reach of the custodians of official teaching. The essence of Christianity had become a set of doctrines and laws articulated and controlled by a hierarchy that saw those doctrines as a divine deposit of truth. Theologians might argue about the articulations with great subtlety and intensity, but in that millennium few would have chosen to engage in basic disagreement over the official teachings, all of which were seen to be corollaries of the basic faith in Jesus Christ as participating in the truth of God and providing the way of salvation.

Through these centuries there was also increasing differentiation between the official clergy, which administered the sacraments and oversaw the body of the faithful, and the laity. Most of what was debated centuries later about the essence of medieval Christianity came from the records of these authorities. As more is learned about the faith of the ordinary believers, it becomes more evident in the records of social history that people offered countless variations on the essence of the faith. Many people used the church’s officially legitimated faith in the power of saints’ relics to develop patterns of dealing with God that, according to the Protestant reformers, detracted from the uniqueness of Jesus Christ as the only agent of salvation.

During this thousand years in both Western and Eastern Christianity, when the faith had a cultural monopoly, there was an outburst of creativity and a fashioning of a Christian culture that greatly enhanced and complicated any once-simple notions of an essence. Christianity was as much a cultural tradition as it was a faith tradition, an assertion that the leadership of the medieval church would not have regarded as diminishing or insulting. Christianity as a cultural tradition is perhaps most vividly revealed in the magnificent cathedrals and churches that were built in the Middle Ages and in the illuminated manuscripts of the period.

As Christian culture grew ever more complex, however, there arose a constant stream of individual reformers who tried to get back to what they thought was its original essence. Among these was St. Francis of Assisi, who in his personal style of devotion and simple way of life was often seen as capturing in his person and teachings more of the original essence of Jesus’ truth and way of salvation than did the ordained authorities in the church and empires. Unlike the Waldenses and members of other dissident groups, Francis accepted the authority of the ordained clergy and contributed to a reform and revival of the broader church.

Britannica Quiz

Pop Quiz: 19 Things to Know About Christianity

In the late Middle Ages a number of dissenters emerged—such as Jan Hus in Bohemia, John Wycliffe in England, and Girolamo Savonarola in Florence—who challenged the teachings of the church in more radical ways than someone like St. Francis did. For all their differences, they were united in their critique of what they thought complicated the essence of Christianity. On biblical prophetic grounds they sought simplicity in the cognitive, moral, and devotional life of Christianity.

When the Protestant Reformation divided Western Christianity—as Eastern Christians, already separated since the 11th century, looked on—the 16th-century European world experienced a foretaste of the infinite Christian variety to come. The reforms that gave rise to the many Protestant bodies—Lutheran, Anglican, Presbyterian, Reformed, Anabaptist, Quaker, and others—were themselves debates over the essence of Christianity. Taken together, they made it increasingly difficult for any one to claim a monopoly on the custodianship of that essence, try as they might. Each new sect offered a partial discernment of a different essence or way of speaking of it, even if the vast majority of Protestants agreed that the essence could be retrieved best, or, indeed uniquely, through recovery of the central message of the Scriptures.

After the ferment of the Reformation, most of the dissenting groups, as they established themselves in various nations, found it necessary to engage in their own narrowing of focus, rendering of precise doctrines, and understanding of divine truth and the way of salvation. Within a century theologians at many Protestant universities were adopting systems that paralleled the old scholasticisms against which some reformers had railed. Those who had once thought that definition of doctrine failed to capture the essence of Christianity were now defining their concept of the essence in doctrinal terms but were doing so for Lutherans, Reformed, Presbyterians, and even more radical dissenters and resistors of creeds, such as the Anabaptists.

The belief of St. Vincent of Lérins that there is a faith that has been held by everyone, always and everywhere, lived on through the proliferation of Protestant denominations and Roman Catholic movements and, in sophisticated ways, has helped animate the modern ecumenical movement. Thus, some have spoken of that movement as a reunion of churches, an idea that carries an implication that they had once been “one,” and a further hint that one included an essence on which people agreed. Reunion, then, would mean a stripping away of accretions, a reducing of the number of arguments, and a refocusing on essentials.