Christianity is in essence a personality cult. At the centre of its message is an individual person, Jesus – and his historical rooting as person in a particular time and place is emphasised by the very ordinariness of that name for the Jewish society into which he was born. “Jesus” is more properly “Jeshua”, the name of an ancient Jewish hero, who appears in Anglophone Christian Bibles as Joshua (no doubt so that Christians may distinguish him from his later namesake). This Mr Average of Galilee has acquired what we might mistake for a surname, so he is called “Jesus Christ”. Yet Christ is not a name but a title, significantly not in the Aramaic which Jesus spoke, but in Greek. It means “the Anointed One” and is the translation of a Hebrew term meaning the same, a word familiar even to those beyond Judaism and Christianity as “Messiah”.

So Christians believe that the Christ who is an aspect of the God who was, is and ever shall be, is at the same time a human being set in historic time. History matters a great deal in Christianity, which is why it is so important to try and get the history right and not to be misled by shoddy versions of it. History was there from the start, given that Jesus would have grown up with a welter of stories about his Jewish past and its significance in God’s purpose, many of them contained in the Hebrew scripture that Christians call the Old Testament. The first surviving specifically Christian literature was a story, or set of stories, about how Jesus died: these are the “Passion narratives”, which are now embedded in the Four Gospels and which are themselves a set of stories seeking to throw different spotlights on the God who was made man. Christians in our own age also believe that they can meet this human being in as real a fashion as the disciples who walked with him in Galilee and saw him die on the cross. They tell stories about themselves on the basis of these stories from the past: more Christian history.

Christian history is also the story of a book, the Christian Bible (which is actually a library of books – the Greek word Biblia is in the plural, meaning “books”). When, in the seventh and eighth centuries AD, the Anglo-Saxons had to create a brand-new vocabulary in their own language for the theory and practice of Christianity, they considered what word they should use to describe this Bible and they came up with “biblioðece”, which is the same word as the French still use for “library”. Books are the storehouses for human ideas and the Bible is no exception: whatever one thinks of its claims to authority, it is the record of one of humankind’s attempts to access and understand the divine.

Ideas are independent variables of the human mind, which need to be taken seriously and understood in their own terms. Christianity has a huge capacity to mutate, like all successful world faiths. Christians do not like being reminded of this, particularly those who are in charge of the various religious institutions which call themselves churches, but that is the reality and has been from the beginning. It will be better for the mental health of the followers of the great religions if they come to recognise this diversity as a virtue and not as a vice, an opportunity and not a threat.

Christianity was a marginal branch of Judaism whose founder, Jesus, left no known written works; Jesus seems to have maintained that the trumpet would sound for the end of time very soon and, in a major break with the culture around him, he told his followers to leave the dead to bury their dead. Yet his followers remarkably quickly seemed to question the idea that history was about to end: they collected and preserved stories about the founder. Within a few decades they also survived a major crisis of confidence at the end of the first century, when the last days did not arrive. This was perhaps one of the greatest turning-points in the Christian story, which shaped it into a very different institution from that of its founder, or even of its great apostle, Paul, complete with an institutional hierarchy, a collection of credal statements and a closed canon of scripture; but we know little about it. Christianity, unlike Judaism, its parent-faith, was not inclined to write about disappointment in its sacred literature.

A basic element in the chameleon-like character of Christianity is an instability, which comes from its twofold ancestry. Far from being simply the pristine, innovative teachings of Jesus Christ, it draws on two much more ancient cultural wellsprings, Greece and Israel. The story must begin among the Ancient Greeks and the Jews, a thousand years before Jesus, hence the title of my book Christianity: the first three thousand years.

That first three thousand years was, in fact, a pair of thousand-year histories, marching side by side. Both Jews and Christians thought they had a uniquely privileged place in the world’s history. The extraordinary cultural achievements in art, philosophy and science of the Ancient Greeks gave them some good reason to think this. More surprising was the fact that the constant experience of misfortune and destruction did not kill the Jews’ faith in their own destiny. Instead, it drove them to conceive of their God not simply as all-powerful, but passionately concerned with their response to him – and passionate in anger as well as love towards them.

Such an intensely personal deity, who was nevertheless the God for all humanity, was very different from the supreme deity who emerged from Greek philosophy in the thought of Plato: all-perfect and, therefore, immune to change and devoid of the passion which denotes change. The first generations of Christians were Jews of the eastern Mediterranean who lived in a Hellenistic world, shaped by Greek elite culture at least from the time of Alexander the Great’s conquests four centuries before. They had to try to fit together these two irreconcilable Jewish and Greek visions of God – and the results have never been and can never be a stable answer to an unending question.

Most Christians alive in the world today are Catholics or Protestants, who together comprise more than 80 per cent of all Christians (if you lump in the Mormons). Another 10 per cent or more call themselves Orthodox, with some other local label attached – Greek Orthodox, Russian Orthodox, Romanian Orthodox and so on. That does not leave much over, as my schoolboy arithmetic tells me. But that sliver of alternative Christianity, the few per cents after you have added up all the Christianities which I have just named, was once the future of the Church. It is the ancient Christianity of Africa and Asia, flourishing still in Ethiopia and India, finding an uneasy place in national life in Egypt, hanging on for dear life elsewhere in the Middle East, or unhappily more often, finding exile in America or Australasia. That is a lost Christian history, which Western Christians need to know.

Because most Christians now are Catholics or Protestants, they give priority to their own history, which is the story of the Western, Latin-speaking Church, once so marginal, so provincial, so unsophisticated in its thinking. But once the outcome looked very different. In the year 451, the Roman emperor, or rather his wife, Pulcheria, a lady with whom it was unwise to trifle, called a council of bishops to a town called Chalcedon. It’s no coincidence that Chalcedon was within easy reach of the imperial palace troops in Constantinople; you can still reach it on the Bosphorus ferry from Pulcheria’s former capital, Istanbul, in 40 minutes or so.

The issue at Chalcedon was a complicated argument about the natures of Jesus Christ: the balance between Jesus, the man, and Christ, the divine Son of God. The imperial government was desperately concerned about this, because the arguments surrounding it threatened to split the empire in two. So the emperor offered the bishops a deal, which was a deliberate compromise: steam-rolling a settlement through the middle of the opposing sides. At the centre of it was what has come to be known as the Chalcedonian Definition of the Natures of Christ. It is what Catholics, Protestants and Orthodox alike classically believe about this matter, which is, after all, at the heart of Christian belief.

In the traditional reading of the history of Christianity, the Council of Chalcedon of 451 has usually been seen as the culmination of the early church’s story: a sort of Hercule Poirot denouement in the drawing-room where, after all the complications of the early church plot, the truth is revealed and then the credits roll. But this story of triumph is an illusion. Chalcedon was a disaster. Fully two-thirds of the church refused to sign up to it, partly because they did not trust the emperor to do theology. Because it was a compromise, those who rejected it were on either wing, so they detested each other as much as they detested the emperor’s church and, as I discovered when filming my history of Christianity in the Middle East, they still do.

So these refuseniks founded their own churches, led by their own bishops; their snooty enemies in the emperor’s church gave them condescending names, Nestorians and Monophysites, and because those names are condescending, it is worth replacing them with admittedly clumsy labels which these Christians might just find acceptable: Dyophysites and Miaphysites. They themselves, of course, would simply call themselves Orthodox. To the people we Westerners call Orthodox, they were and are unorthodox. Yet they are still with us. Once it seemed as if they and not the church of the Roman and Byzantine emperor would be the future. But instead, the emperor’s church has descended into Roman Catholicism, Protestantism, Orthodoxy.

The outcome was long in the balance. It was much swayed by the astonishingly rapid early conquests of the Muslims in the seventh century; yet the first Muslim rulers did not regard their enterprise as promoting their faith in a missionary manner and, in fact, Dyophysite Christianity flourished under their rule. When the Abbasid dynasty founded a great new Muslim capital and named it Baghdad, Dyophysites provided much of its intellectual life. The Dyophysite church of the East was a think-tank for the Muslim Abbasids in Baghdad. Because the church of the East was so used to arguing about the natures of Christ with other Christians and so adept at translating Greek philosophy and theology into its own Syriac language, it had all the intellectual equipment which the Arab Muslim rulers needed to access the wisdom of the past. Without the church of the East and its translation of Mediterranean Greek classics into Arabic, we would not have regained our access to much Greek philosophy, or even got to know about what we in the West call Arabic numerals (they actually came from India).

And the church of the Middle East became the church of the Far East. It reached to China. Outside the ancient imperial capital, now called Xi’an, in the heart of the Chinese countryside, you can stand in the precinct of a Christian monastery from the seventh century, still called by the Chinese phrase for the Roman Empire, Ta Qin. It is possible that there might be similar experiences on offer in Korea and even in Kyoto in Japan, transformed into Buddhist shrines. But steadily, bit by bit, this future of Christianity was eroded. Plague, massacre, victimisation by mad or bad monarchs; Islam faced all these disasters too, but in the worst times, Islam found more powerful friends in Asia than the Christians. It might have taken just one more Mongol warlord to listen to his Dyophysite Christian mother or sister and central Asia would have become Christian rather than Muslim; but it was not to be. Bishops in Tibet found no successors and monasteries in Mongolia crumbled into dust.

Into the vacuum stepped others: in particular, the bishop of Rome, the pope. In my Christianity: the first three thousand years, I describe the millennium from the fifth century as “the unpredictable rise of Rome”, during which a common Latin language for liturgy and a shared legal system emerged. Western Europeans who know anything about their history tend to take this united medieval phase of it for granted, in the way that, when we are growing up, we take for granted the environment around us as the norm by which everything else is judged. But this obscures the fact that it is unique in human history for a region to be so dominated by a single form of monotheistic religion and its accompanying culture for a thousand-year period. Only Saudi Arabia comes close to it, for a far shorter period, and it would be very hard to name another example.

The lesson to learn from this is that there was nothing inevitable about the modern papacy and the claims that it makes for its special authority have only been remotely plausible for about half Christianity’s history. The early church looked to five patriarchs, not one, and there is still another pope in Alexandria. It has not been good for the spiritual health of the Roman Church to look to a single leader, however much it helped to pack the pews throughout the world in the last century. Moreover, the more recent history of the Roman Catholic Church (that part of the Western church which remained loyal to the pope in the 16th century) contains a paradox: from the early 19th century, popes became more autocratic, just at the time when, through most of Europe, autocracy was giving way to democracy. The Catholic Church turned its back on a medieval “conciliarist” current of thought, which stressed a much wider sharing of power and decision-making, through councils of church leaders and maybe even laypeople.

The accident of the French Revolution severely crippled the power of rival focuses of authority within the church: it had destroyed the Holy Roman Empire, removing its emperor and the prince-bishops, who had had a tendency to treat papal claims to monarchy with a sceptical eye. Now the pope stood alone like a post when the rest of the building has collapsed. Recent papal claims to authority are based on that historical circumstance. In the wake of the second Vatican Council of the 1960s, we have witnessed half a century of struggle between Catholics who wish to defend that papal monarchy and those who wish to restore the conciliarist programme.

Is it worth the effort to refocus the history of Christianity in such ways as these? Emphatically yes – because, in the last 40 years, religion has thrust itself into the consciousness even of secular Europe. When I was an undergraduate at the end of the 1960s, the future of religion was commonly yoked to the word “secularisation”: the assumption that religion’s power to influence the mind of humanity was waning in the face of increasingly secular-minded societies and that it would retire gracefully out of the political or public world into the private sphere. But in 1977, the US elected the first born-again Christian president; in 1978, there came a counter-reformation pope, John Paul II; and, in 1979, the ayatollahs seized control of the Iranian Revolution. I could extend the chronology year by year into a relentless succession of events. Europe, far from setting the pattern for the world in secularisation, has proved the exception to the worldwide self-assertion of religion. One or another form of religion matters desperately to the overwhelming majority of human beings alive and, if historians ignore that plain fact, they are ignoring reality.

I also think of modern worldwide controversies which historians may help to unravel. Take the furious modern rows about sexuality. At the present day, many conservative evangelical Protestants refuse to accept new configurations of human sexuality, in the name of faithfulness to the Bible. What they often fail to notice is that they have already assisted in one major rejection of biblical authority, one of the most significant so far in the history of Christianity. In the 18th and 19th centuries, a crucial minority of evangelicals successfully campaigned for the abolition of slavery, in defiance of that same Bible, in which there is a clear and consistent acceptance of the permanent existence of slavery. The same evangelicals who proclaim biblical certainties are proud of an achievement which defied biblical certainties. This will not be the last occasion on which there will be such a dramatic change of direction. Christianity is a mere 2,000 years old, a tiny fraction of human experience over millennia. It is a young religion, finding its way; that is what makes it exciting to contemplate.

It is always worth emphasising the diversity and the unexpected, crab-wise evolution of Christianity, or indeed of any religious system. One of the most unattractive features of a certain sort of religious outlook is its insistence that it represents the only true or authentic face of the religion of which it is a part. Of course, this is not the exclusive property of religion. As one contemporary observer of the French Revolution sardonically commented, the Jacobin slogan “fraternity or death” might more accurately be understood as “be my brother or I’ll kill you”. One could read the history of the world after the French Revolution in terms of the tidy-mindedness of certain pathological forms of the Enlightenment: a dogmatism which fuelled fascism and Stalinism and has brought measureless misery to the world.

This common human pathology of dogmatism, religious or non-religious, is based on pride. The most plausible doctrine of Western Christianity, depressingly, is original sin; and, at the root of all sin, is pride. If historians are prophets (and they should be, in the original meaning of the Hebrew equivalent of that word, “spokespeople”), then their principal prophecy is against pride. Pride is also the target of the court jester. The good historian and the successful court jester have much to say to each other.

This essay originally appeared in ‘Knowledge and Information – Perspectives from Engelsberg Seminar, 2018’, Bokförlaget Stolpe, in collaboration with the Axel and Margaret Ax:son Johnson Foundation.