For some, probably most, the Covid-19 pandemic is a question of massive mitigation. The aim is to learn lessons and return to business as usual, as soon as possible. For others, it's different. It's not just a disaster to get through, but a moment to seize and change the world.

The latter response interests me. It raises the question of what it takes to reimagine life along all its variables: economic and political, educational and existential, ecological and social and spiritual. It's no mean undertaking.
However, history provides case studies. There have been moments when civilisations have pivoted. The one I have in mind, moreover, seems to have shifted because climate change and pestilence were grim catalysts of transformation.

In the third century CE, Christianity emerged into history. It stepped out of the shadows to become a mass phenomenon. There may have been 100,000 Christians in 200 CE. By 300 CE, there were probably around 3,000,000, which in some territories meant Christians accounted for up to 20 per cent of the Roman empire's population. And the rest is, indeed, history.

But what did it take to precipitate that transformation? And what does it suggest about the possibility of civilizational change now?

It's a complex question, of course, one that can only spark debate, not admit easy answers. But I think there's good evidence that one element was key. Christianity had what it took to seize the moment and change the world because it offered a new sense of what it is to be human. Moreover, that sense was accessible to the masses.

Part of the story has recently been retold by the historian of antiquity, Kyle Harper. In his brilliant book, The Fate of Rome: Climate, Disease and the End of an Empire (Princeton University Press, 2017), he presents the case for factoring in the devastating impact of climate change and plague on the Roman system. He gathers the evidence and shows that the moral degeneracy highlighted in Edward Gibbon's Decline and Fall, and the bureaucratic overstretch favoured by more recent historians, probably weren't the key drivers.

Rather, it's a case of nature thwarting human ambition. Solar cycles and volcanic eruptions, pestilence and viruses, were the ruinous agents. They were felt as an environmental stress that eventually defeated pagan Rome's longstanding hold on the Mediterranean world.

But that is only half of the story. Collapse is one thing. Regeneration is something else entirely. Here is where the genius of Christianity comes in.

Consider the most important church figure in the century of Christianity's appearance. Cyprian was the bishop of Carthage from 248-258 CE. A prolific writer and gifted rhetorician, he read the moment and deployed the weapons of critique that he had in his arsenal.

He could see that the fabric of empire was stretched, if not crumbling. Along the frontiers of the Danube, Euphrates, Rhine and Nile – which is to say, north, south, east and west – emperors faced potentially catastrophic threats. The moment of weakness became Cyprian's opportunity.

He preached about living in "an old age of the world". He was drawing on the medical wisdom of Galen, which interpreted old age as the gradual evaporation of warmth and vitality. The implication was that Roman civilisation had become decrepit.

It lacked spiritual vitality, for all that emperors tried to conceal it behind the exercise of power. It was out of ideas, which leaders tried to paper over with pageants of games and grandiose building projects. It lacked joy in its soul, which is why people became addicted to peak experiences and carnal pleasures. To instil order and discipline, Rome relied on law not friendship, the army not loyalty, and compulsory cult practices, not the natural love of the gods.

Cyprian also spoke of the skies turning grey, the earth becoming thirsty, and the rains failing, which he probably literally felt, along with his listeners. The evidence now is that the climate did change during his lifetime. For example, in 244, 245 and 246 the Nile flooded weakly or not at all, compromising the productivity of Rome's breadbasket, Egypt.

And then there was the pestilence, now known as the Plague of Cyprian. From the descriptions that survive, it seems most likely that it was caused by a filovirus, from the family of pathogens that includes Ebola. Disease spread across the empire in two years and raged for about fifteen, from 249 CE. Cyprian described it: "the strength of the body is dissolved, the bowels dissipate in a flow, a fire that begins in the inmost depths burns up into wounds in the throat, the intestines are shaken with continuous vomiting, the eyes are set on fire with the force of the blood, the deadly putrefaction cuts off the feet."

At its peak, 5,000 people died in Rome every day.

The combination of pestilence and crop failure was a religious as well as civic crisis. Harper describes how emperors minted coins calling on "Apollo the Healer". The Sibylline books were inspected. It seems likely that in 249 CE, the emperor, Decius, required all citizens to share in a civic act of sacrifice. It was an early response to the outbreak. Some Christians who refused were charged with defiance and grotesque social irresponsibility.

"The combination of pestilence and persecution seems to have hastened the spread of Christianity," Harper writes.

But that brings me back to my initial question. What did Christianity have that enabled Cyprian and others to turn a moment of hideous suffering and dire threat into an opportunity for growth?

The standard answer is moral. In short, Christians cared. For example, Rodney Stark in The Rise of Christianity, describes how Christians remained in afflicted cities when others fled, and cared for the sick and dying. That was impressive and also had a real effect. Cleaning and hydrating sufferers increased their chances of survival.

Harper reflects this understanding, too.

"Christianity's sharpest advantage was its inexhaustible ability to forge kinship-networks among perfect strangers based on an ethic of sacrificial love," he writes.

But this remark begs a factor that's crucial to highlight. I think it's determinative. It underpins the ethic of sacrificial love and makes its practice possible.

Put it like this, I don't believe that the Romans were a heartless breed who cared nothing for human suffering. Contrary to popular opinion, they were not beasts. Many writers, such as Cicero, worried about the violence of gladiatorial games, for example, and the Roman world knew about caring for others. For example, in 212 CE, Caracalla had granted citizenship to all free inhabitants of the empire. It was no trivial offer. The relationship between manumitted slaves and patrons was upended. Woman claimed new property rights. Bread became the key handout of a massive welfare state.

What was different now was that Christianity was able to launch an existential revolution. The crucial shift is implicit in what Harper describes as its new networks of "perfect strangers". This was the secret ingredient that enabled Christianity to seize the moment and launch a civilizational change.

The issue is what enabled those new networks to form. Previously, social networks had been based either on family and kin, or city and citizenship. Hence, the significance of Caracalla's citizen-based enfranchisement. But Christianity developed the perception that the bonds of family and citizenship had been eclipsed. It did this by showing people that the human individual now had access to the deepest level of reality from within themselves.

Its innovation was to celebrate the life of one person, Jesus of Nazareth, and insist that his humanity, not his birthplace or status, was the locus of complete and unmediated access to God. As the philosopher, Larry Siedentop, puts it: Christianity "provided an ontological foundation for 'the individual'".

The new individuality was grounded in God, enabling individuals to demonstrate acts of sacrificial love for others rooted in relationships that had nothing to do with kin or state. Christians felt that they were spiritually sisters and brothers, and that they belonged to "another country", a new ethnos or nation, metaphors that emerge early in Christianity.

Preachers such as Paul quickly realised that Jesus pioneered a new way. What was required was response. The individual could aspire to a sense of themselves based upon choice and agency, not fate and duty. "There is no longer Jew or Greek, there is no longer slave or free, there is no longer male or female," he wrote in an astonishing passage.

Instead, Christianity offered a freedom based upon a sense of self that didn't erase older civic distinctions and religious markers but simply leapt over them. In their inner lives, the individual could transcend cult and position altogether.

As a result, notions such as individual free will and personal conscience emerge as subjects of dispute and discussion among early Christian thinkers. They also developed the idea of resurrection in the face of death. The new individual could hope for postmortem fulfilment, a spiritual body and religious satisfaction in the afterlife, not a dreary retirement to a land of shades. But to hope for these things in the world to come, you need a strong sense of individuality in this world. Christianity rewrote the implication that unless you are a hero or an emperor, you are a poorly differentiated player in the social collective.

The path to Christianity's cultural dominance was not straightforward, of course. The persecutions of Diocletian, in the century that followed Cyprian, were fierce, though mostly because Christianity was now a force to be reckoned with.

Then, when the "new empire" bedded down after the crises of the third century, under Constantine, Christianity became the unofficial and then official religion in part because it best expressed how a majority now felt. People had caught on to its penetrating consciousness of human individuality. Whatever else led Constantine to adopt the new faith, it was a canny move. It secured him the longest reign of a Roman emperor since Augustus.

This is the lesson I learn from the civilizational change that is historic Christianity. As a case study, it suggests that to change the world and reimagine life takes more than economic decline or environmental disaster, war or plague, though these may rock societies and systems to the core. It also takes more than redesign or hacking, upgrade or reprogramming. It's not fundamentally a matter of making sense of the emergency, or cognitively bootstrapping yourself out of the modern meaning crisis.

Transformation requires literal inspiration and radical vision: a new spirit. Civilisations change with a fresh perception of what it is to be human, a revolution of consciousness, and renewed awareness of humankind's relationship to the interiority of the cosmos, natural and divine. It requires the makings of a new ethnos, anthropology, and probably religion.

That doesn't happen very often in a way that lasts. But in these weeks of stress, these months of instability, we can attend to events and listen. We can be open. Of ourselves, we can't forge a path beyond a return to business as usual. But we can keep watch for any signs of a new unveiling and align with them.

Mark Vernon has written about the emergence of Christianity in his recent book, A Secret History of Christianity (John Hunt Publishing). See www.markvernon.com