Why? Those with an interest in first-century Rome and the origins of Christianity always and ever must return to this question. Why, out of all the other minor deities that flourished at the birth of Rome's empire, did the jealous god of a small, dangerously restive province become the one that Rome would pick three centuries later to control its own restive population?
Why not the embrace cult of Isis, far more popular? Why not follow the teachings of the Stoics, or of Zoroaster, neither of which required that their followers become martyrs? Why not the Buddha, Confucius, Apollonius? What did Christianity have that made it uniquely suitable?
Selina O'Grady, producer of the BBC's moral documentary series Heart of the Matter, is well-placed to answer this question. Armed with a coherent time-line and some exceptionally lucid maps, her latest work sets out the nature of society and religion in the first century AD.
She starts with Augustus, who made himself both emperor and god while telling the Senate that he was doing neither. His spin was masterful, only let down by his successors who tarnished the brand of imperial deity to the point where it became a laughing stock. He wasn't alone in being a man who called himself a god. His neighbour, the Candace (Queen or Queen Mother) Amanierenas, ruled as hereditary God/Queen of what was then Meroe and is now southern Egypt/northern Sudan. At the conclusion of their war, which by all rational measures she had lost, she sent him a sheaf of golden arrows, stating that if he wanted peace, they were a token of friendship, but if he wanted war, he would need them. Augustus backed down and sued for peace; in the realms of men-become-gods, lineage mattered and Augustus was a parvenu.
In some parts of the world, god-rulers were not permissible. Herod the Great, client king in Judaea, endeavoured to bring Roman culture to his people and ended up slaughtering them to keep himself safe. Yaweh was a jealous god who brooked no rivals, and the Pharisees were in the process of bringing his worship into the home. Where, previously, the Sadducees had preached a distant deity who set rules to which only the hereditary priestly class could possibly adhere, the Pharisees preached an oral tradition that allowed more flexibility of worship, but brought with it responsibility. Because it was now possible for all good Jews to follow the rules laid down by their god, so it was necessary – and that meant they must not acknowledge Caesar as a god.
This intransigence led ultimately to the destruction of Jerusalem and allowed the rantings of an apostate – Paul – to usurp the original teaching of a man he had never met and turn it into a state religion.
O'Grady takes us on a detailed tour of the philosophies, cults and religions available to the Roman citizen, from Stoicism to Buddhism. In Rome, the cult of Isis offered a personal god, a community of worship and a sense of an afterlife. The worship of Mithras, which offered much the same, grew in the second century and so is not covered, a source of sorrow to those of us who find Mithras a more congenial god than Yaweh. Perhaps that's for another book.
There would be room, also, for another book covering the circumstances under which the Christianity came to be taken on by Constantine. I came away understanding vastly more of the options on offer, but without truly understanding what it was about Christianity that made it so perfectly suited to the Roman state's control of its population.
This should not, however, detract from a masterful narrative, clearly told, with great panache, insight and humour. It should be required reading for anyone, Christian or otherwise, who has an interest in the historical context in which the "mystery cult of Yaweh" became one of the dominant forces in the world.