Andrew Walls was mildly incredulous when I phoned him in Aberdeen, Scotland, to ask for an interview. Of course he would gladly help me, he said in a restrained Scotch brogue, but was I sure I had the right person? He couldn't understand why Christianity Today would want to write about him.

The reason is simple: Andrew Walls may be the most important person you don't know. Most Americans and Europeans think of Christianity as a Western religion. Prominent leaders of the last 50 years, like Billy Graham, Oral Roberts, and Pope John Paul II, are known primarily for their influence in the West, though in fact each of them has played a significant role in wider, global Christianity. But the most important development for the church in the 20th and 21st centuries has not been in the West at all, but in the astonishing shift of Christianity's center of gravity from the Western industrialized nations to Asia, Africa, and Latin America. In a short time, Christianity has been transformed from a European religion to a global one.

Andrew Walls is the person to help us understand what this means. One of the first scholars to notice and study the shift, he combines exhaustive knowledge of the worldwide church with a deep historical and theological vision. Scholars who know his work (almost all published in obscure journals) speak of him with something like reverence.

"Andrew was a pioneer," says Yale University historian Lamin Sanneh. "He is one of the few scholars who saw that African Christianity was not just an exotic, curious phenomenon in an obscure part of the world, but that African Christianity might be the shape of things to come." American church historian Mark Noll says that "no one has written with greater wisdom about what it means for the Western Christian religion to become the global Christian religion than Andrew Walls."

Walls's insights go even deeper than that, probing Christian history to gain a prophetic vision of what "Christian" really means across an extraordinary diversity of times and cultures.

Love Affair with Africa

I met Walls for a daylong conversation at the Overseas Ministries Study Center (OMSC) in New Haven, Connecticut. It is a place he visits frequently, living mostly on oatmeal he cooks in an upstairs kitchen. Walls is nearly 80 now, living on "injury time" as he puts it, borrowing the soccer term. He has had several heart attacks and 20 years ago seemed close to death, but as Sanneh says, "Andrew is hard to stop." Retired from his university posts, he keeps up an impossible schedule of travel, lecturing all over the world.

He is an instinctive activist, but not on behalf of himself. Though a wonderful writer, he has produced no books and nothing like a magisterial summary of his work. Two collections of essays offer the best introduction to his work, but Walls himself had almost no involvement in bringing the books to birth—his friends did it. "He's known by his students," Sanneh says, "and for him that's good enough." Adds Jonathan Bonk, executive director of the OMSC, "His magnum opus is people."

Walls went to Africa in 1957, a 29-year-old veteran of Oxford and Cambridge planning to fulfill his missionary call through teaching church history at Fourah Bay College. In the sleepy tropical warmth of Freetown, Sierra Leone, fellow Britons took him in hand but painted a depressing picture of the local church. The Methodists, Walls was told, had only "two young men, one 48, one 54" entering study for ordination that year. Walls's students wrote down everything he said, but "you could see from their faces that it didn't penetrate." Freetown was a colonial outpost where Europeans could live "between the office and the club," awaiting "the arrival of the fortnightly mail boat."

Most Westerners viewed the African church as a weak imitation of the European, struggling to grasp theological truths, struggling even to sing hymns properly. As yet, nobody noticed the signs of titanic growth.

Walls was too curious to stick to the European compound. He preached in village churches and participated in local preachers' meetings. He began to study local church history. "Real church history" involved Greek and Latin, he believed then, but as a hobby he figured he ought to learn about the locals.

His first stunning revelation came in the classroom, where he was teaching about the early church. "I still remember the force with which one day the realization struck me that I, while happily pontificating on that patchwork quilt of diverse fragments that constitutes second-century Christian literature, was actually living in a second-century church," he explains. "Why did I not stop pontificating and observe what was going on?"

It was a move from "talking about texts" to "talking about the community that formed the texts." The epiphany transformed his understanding of both the church in Sierra Leone and the second-century church he had studied in the Bodleian Library at Oxford. "As I looked at the surviving literature of the early second century, I could see all the examples of that literature around me," Walls says. "You read the first letter of Clement, and, yes, I'd hear sermons like that, and just as long. You read Ignatius, and though I had not actually seen anybody going to martyrdom, you saw the same sort of intensity."

What he met in Sierra Leone was not, Walls realized, a derivative or younger version of the European church, but "a symbiosis, very carefully fused." Something was occurring that paralleled the patristic period, when a Jewish gospel got translated into Greco-Roman culture. For Walls, this brought a "very definite movement from depression to hope" and began a lifetime love affair with Africa.

The Indigenous Church

After five years in Sierra Leone, Walls and his family—his wife, Doreen, and two small children—moved to Nsukka, Nigeria, where Walls headed up the religion department in a new university. He was beginning to grasp the dynamism of the African church. On one enormous wall, he and a colleague created a map of East Nigeria and endeavored to record every last place of worship. They began to collect old church registers.

"We were first told there weren't any," he recalls. "'The documents are kept in heaven,' or they were all eaten by termites. 'Nobody keeps records.' [But] in fact, we found hundreds and hundreds of baptismal registers, marriage registers, discipline books, and committee minute books. Some of them went back to the 1880s. It was an African church with African executives, keeping its records with varying degrees of efficiency, according to the degree of education of the people involved But there it was: working, witnessing, worshiping, sinning, repenting. All this going on for a 70- or 80-year period."

Walls learned of vast revival movements, of foundational preachers and evangelists, of extensive church networks with their own ideas about order and their own ways of viewing Scripture. (For example, some saw Leviticus as among the most important books in the Bible.)

He left Nigeria in 1966, weeks before civil war erupted. While he was gone, the library burned, and he lost the entire collection of church materials. He returned to Africa at least once annually over the next 40 years, but never again to live. Instead, at the University of Aberdeen and later at the University of Edinburgh, he drew scholars from all over the world to learn with him.

The Martian Visit

Decades later, Walls still vividly remembers the contrast between the vibrant African church and the dwindling vitality he found at home in Scotland. Faculty meetings were desperately dull, mainly because "nobody wanted anything." Church buildings were being turned into bars. At Aberdeen, theological students took three years of church history: early church, Reformation, and Scottish. Ten years before, Walls would have approached such a curriculum with zest. Now it seemed hopelessly inadequate.

In Walls's second year home, he presented a lecture to the combined divinity faculty of the four Scottish universities, comparing the Church of Scotland to its "daughter," the Presbyterian Church of Nigeria. He also offered the first version of what he would eventually call "the Martian visit." (You can read a later version in Walls's remarkable collection of essays, The Missionary Movement in Christian History.)

In it, he imagines a space visitor who comes to earth to study representative Christians over the centuries. He begins with Jewish believers in the first century, fond of large families and still worshiping in the temple. He then jumps ahead to Roman Empire believers, horrified at the idea of animal sacrifice and expecting church leaders to be celibate.

On a third visit, he meets Irish Christians standing up to their necks in ice-cold water reciting psalms. Then come English Christians of the 18th and 19th centuries, whose idea of holiness is not ice-water asceticism but activism for missions and against slavery. Lastly, he visits Nigeria in the 20th century to meet white-robed Christians dancing and chanting in the streets, claiming to be cherubim and seraphim. What, Walls asked, do they all have in common?

Walls had begun to see churches in Africa and Scotland as part of a bigger story. How is the faith transmitted and transformed across cultures? Through what process does the rationalistic faith of Scottish Christians become the visionary, supernaturalized life of Nigerians?

Evangelicals believe in the conversion of individuals, but Walls began to see that conversion refers also to nations and communities. Did not the Great Commission command the discipling of the nations? "Conversion to Christ does not isolate the convert from his or her community," Walls says. "It begins the conversion of that community. … [D]iscipling is a long process—it takes generations. Christian proclamation is for the children and grandchildren of the people who hear it."

Walls began to think that this kind of Christian conversion is necessary in every place and time, and that Christian history is the story of how faith moves from one culture to another, translating and retranslating the gospel along the way. (From this view, most of what passes for church history is merely a single European chapter in a much larger book.)

The spread of the gospel is often presented as inexorable progress outward, like an inkblot, but Walls saw that time and again the real story was of ebb and flow. The loss of Christian territory happened not just on the periphery but at the heartland. Jerusalem was the first heartland until the Romans leveled it, and the Jewish church all but ceased to exist. Then came Rome, until the northern Vandals sacked it; Constantinople, until Islam overran it; northern Europe, before Enlightenment skepticism cut its heart out. At each turning point, the gospel made a great escape, crossing over into an unknown culture just before disaster struck. History suggested that Christianity lives by this pilgrim principle.

Not only that, but Walls's study of Paul's letter to the Ephesians suggested that each culture adds new riches to an understanding of Christ, so that "the whole measure of the fullness of Christ" (Eph. 4:13) becomes possible only when bringing all of our different communities together. Each culture asks different questions of the gospel, and as new answers to those questions are unearthed, they enrich our understanding of the greatness of Christ. The second-century church asked philosophical questions that would never have occurred to Jews in Jerusalem. One result was the fourth-century Nicene Creed. Africa asks questions about witchcraft that children of the Enlightenment can't answer. Perhaps a new understanding of Jesus' victory over evil is in the works.

All this is to say that the gospel never stands outside our lives; it must enter human culture and be translated into the local language. It is not static or impersonal, because it is always in the process of being more fully discovered. Mission is not so much a matter of contextualizing the gospel as learning its truth through an entirely new way of life and thought. That process is happening today in overdrive.

While some scholars such as Philip Jenkins emphasize a shift of power from Western churches to those south of the equator, Walls sees instead a new polycentrism: the riches of a hundred places learning from each other. That is why he has delighted in the Centre for the Study of Christianity in the Non-Western World, which he founded at the University of Edinburgh. Students come from all over the world to share what they are learning and to study together. As Kwame Bediako, former director of the Oxford Centre for Mission Studies, puts it, "The gospel that was in principle universal has now become in reality universal."

Tim Stafford is a CT senior writer.