THERE is a moment of crisis in the history of the world’s great faiths. In each case, it was a turning point, challenging believers to define their deepest ideals and ask whether the path they were taking led there. The faith eventually emerged refined, renewed, but only after great anguish and bloodshed.

That crisis hit Europe in the 16th and 17th centuries when, after the Reformation, hitherto suppressed conflicts exploded into violence. Europe was convulsed by war, which ended only after the Treaty of Westphalia in 1648.

That earthquake sent tremors through the minds of good and thoughtful people. What they asked themselves was not “Can God exist amid such suffering?” but “Can the people of God live together in peace?” In that reverberating question were born the great developments of the modern world: the slow separation of religion and power, Church and State, and the gradual independence of science and the academy from faith and its citadels. Had that not happened, Europe would never have achieved the pre-eminence it later held. It would still be trapped in the circle of self-destruction.

Oddly enough, the de-politicisation of religion did not rob it of its strength. It became, if anything, more influential but in a different way. It sanctified marriage and consecrated the family. It motivated people to philanthropy and acts of kindness. It sustained communities, binding neighbours and strangers in reciprocal responsibility. It taught people self-restraint, allowing them to live together in trust (Remember when people could leave their homes and places of worship unlocked?). It made sense of the notion of the common good.

Yet the idea that people could have arrived at that outcome without prior conflict flies in the face of history. We sometimes forget Europe’s pre-modern history, with its massacres, expulsions, inquisitions and burnings at the stake. When Christian forces conquered Jerusalem in the First Crusade they proceeded systematically to murder its Jewish and Muslim inhabitants, men, women and children. The Second Crusade began, as had the first, with a series of massacres of Jews in Northern Europe, for the greater glory of God.

In 1532 Pizarro conquered the Inca kingdom of Atahualpa, seizing its gold and devastating its population. Before executing him, Pizarro told Atahualpa: “We come to conquer this land . . . that all may come to a knowledge of God and of His Holy Catholic faith; and by reason of our good mission, God the Creator of Heaven and Earth and of all things in them, permits this in order that you may know Him and come out from the bestial and diabolical life that you lead.” Faith, what evil is committed in your name.

What then led to crisis and the need to find a new way? Sadly, the historic evidence suggests that error remains undisturbed for as long as religious believers murder their enemies. It is only when they realise that they are killing their fellow believers that the shock of recognition takes place.

What made the 17th century a turning point was that it was a war — a series of wars — of Christian against Christian. As Abraham Lincoln said during another crisis, the US civil war, “Both read the same Bible and pray to the same God, and each invokes His aid against the other.” Only then does soul-searching become inescapable and the long, hard road to peace begin.

Judaism went through a similar crisis 16 centuries earlier. Josephus, an eyewitness of the fall of Jerusalem to the Romans in 70 CE, has left a chilling picture of the Jews inside the city walls, more intent on killing one another than confronting the enemy outside. The result was tragic. In its aftermath, however, Judaism became one of the most pacific of faiths.

Abandoning the sword in favour of the Book, it became a religion of home, synagogue and school. Why did this happen in Judaism some 16 centuries before it occurred in Christianity? Perhaps because Judaism is some 16 centuries older than Christianity. A clock seems to tick in the history of religions, sending crisis in the middle of their second millennium.

When it happens to a great religion, it is a world-changing event. The outcome is predictable: a painful, necessary divorce of religion from power. What is not predictable is how long it takes, and at what price.

Rabbi Sir Jonathan Sacks is the Chief Rabbi of the United Hebrew Congregations of the Commonwealth