Magic, however, has powerful charms. Not long ago I was with a group of ministers on the East Coast. The conversation turned to critical interpretations of the New Testament. I remarked that I did not see how people could make sense of the Bible if they were taught to think of it as a collection of ancient Associated Press reports. (Cana, Galilee — In a surprise development yesterday at a local wedding, Jesus of Nazareth transformed water into wine. . . .) “That’s your critical reading of the Gospels,” one minister replied, “but in the pulpit I can’t do that.” “Why?” I asked. “Because,” he said, “you can’t mess with Jesus.”

Well. If the power of Jesus — “the Christ, the Son of the living God,” as Peter called him — cannot survive a bit of biblical criticism, then the whole enterprise is rather more rickety than one might have supposed. Still, the objecting cleric’s remark illuminates one of the issues facing not only Christians but the broader world: To what extent should holy books be read and interpreted critically and with a sense of the context in which they were written, rather than taken literally? To later generations of the faithful, what was written in fluctuating circumstances has assumed the status of immutable truth. Otherwise perfectly rational people think of Jesus’ Ascension into heaven on the 40th day after Easter to be as historical an event as the sounding of the opening bell at the New York Stock Exchange. To suggest that such supernatural stories are allegorical can be considered a radical position in even the most liberal precincts of the Christian world. But the Bible was not FedExed from heaven, nor did the Lord God of Hosts send a PDF or a link to Scripture. Properly understood — and MacCulloch’s book is a landmark contribution to that understanding — Christianity cannot be seen as a force beyond history, for it was conceived and is practiced according to historical bounds and within human limitations. Yes, faith requires, in Coleridge’s formulation, a willing suspension of disbelief; I do it myself, all the time. But that is a different thing from the suspension of reason and critical intelligence — faculties that tell us that something is not necessarily the case simply because it is written down somewhere or repeated over and over.

Which brings us to the significance of the history of Christianity, and to the relevance of MacCulloch’s book. The story of how the faith came to be is a vast and complex tale of classical philosophy and Jewish tradition, of fantastical visions and cold calculations, of loving sacrifices and imperial ambitions. It was, as Wellington said of Waterloo, a close-run thing: a world religion founded on the brief public ministry, trial and execution of a single Jew in a remote corner of the Roman Empire. In my view, an unexamined faith is not worth having, for fundamentalism and uncritical certitude entail the rejection of one of the great human gifts: that of free will, of the liberty to make up our own minds based on evidence and tradition and reason. John’s Gospel says that “ye shall know the truth, and the truth shall make you free.” Perhaps; I do not know. (No one does; as Paul said, we can only see through a glass, darkly.) But I do know this: Short of the end of all things, it is the knowledge of the history of the faith that can make us free from literalism and ­fundamentalism.

It is difficult to imagine a more comprehensive and surprisingly accessible volume on the subject than MacCulloch’s. This is not a book to be taken lightly; it is more than 1,100 pages, and its bulk makes it hard to take anyplace at all. Want a refresher on the rise of the papacy? It is here. On Charlemagne and Carolingians? That is here, too. On the Fourth Crusade and its aftermath? Look no farther.

To me the appeal of the book lies in its illuminating explications of things so apparently obvious that they would seem to require no explanation. How many common readers could immediately discuss the etymology and significance of the word “Israel”? It comes from a stranger who wrestled Jacob and found him to be admirably resilient. Hence Jacob was given the name Israel, or “He Who Strives With God.” Or would know that Emmaus, the scene of the risen Jesus’ revelation of himself to two disciples over bread and wine, may not have been an actual village in first-century Judea but rather an allusion to another Emmaus, two centuries before, the site of the first victory of the Maccabees over the enemies of Israel, a place where, in the words of the author of I Maccabees, “all the gentiles will know that there is one who redeems and saves Israel”? Or, in a wonderfully revealing insight of MacCulloch’s, that the “daily bread” for which countless Christians ask in the Lord’s Prayer is not what most people think it is, a humble plea for sustenance. “Daily” is the common translation of the Greek word epiousios, which in fact means “of extra substance” or “for the morrow.” As MacCulloch explains, epiousios “may point to the new time of the coming kingdom: there must be a new provision when God’s people are hungry in this new time — yet the provision for the morrow must come now, because the kingdom is about to arrive.” We are a long way from bedtime prayers here.

So how did Christianity happen? In fulfillment of the book’s provocative subtitle, MacCulloch begins his tale in remote antiquity, with the Greek search for meaning and order, the Jewish experience of a fickle but singular Yahweh and the very practical impact of Rome’s early globalism. The predominant peace forged by the empire made the spread of ideas, including Christian ones, all the easier. Politics mattered enormously, and the faith’s temporal good fortune began even before the early fourth century, when Constantine decided that the Christian God was the patron of his military victories. As a tiny minority in the Roman world, Christians knew they could not choose their friends: an early supporter of Christians at court was Marcia, the emperor Commodus’ mistress and the woman who instigated his assassination. Accommodations with the princes of the world drove the rise of the faith, and the will to both religious and political power corrupted it, too. “For most of its existence, Christianity has been the most intolerant of world faiths,” MacCulloch says, “doing its best to eliminate all competitors, with Judaism a qualified exception.”

Powerful allies were crucial, but so was the Apostle Paul, whose writings make up the oldest sections of the New Testament. Partly because of the expectation of the imminent coming of the kingdom, Christianity, MacCulloch writes, “was not usually going to make a radical challenge to existing social distinctions.” Hence Paul’s explicit support for slavery. “Everyone should remain in the state in which he was called,” Paul wrote, and his Epistle to Philemon was, MacCulloch says, “a Christian foundation document in the justification of slavery.”