“The Reformation began,” according to a sermon I once heard, “when a Catholic priest found a Catholic doctrine in a Catholic book.” The priest was Luther; the book was the Bible; the doctrine was salvation by grace. All true, as modern scholarship attests. So how did Europe get riven by confessional fault-lines?

Diarmaid MacCulloch’s answer is so long that he may never reach his target audience: the “general reader” will prefer Patrick Collinson’s concise, rounded recent book. But MacCulloch deserves readers. His message fits into a few bold, brief claims. The Reformation was the experience of people assigning to themselves, in unprecedented numbers, a place in “a cosmic drama plotted by God”. Intellectually, it was “a new statement” of St Augustine’s theology. Socially, it was all about sex: an attempt by the godly to control lay love-lives. These three themes were the common history of the Catholic and Protestant traditions and there was nothing inherently divisive about them. But for an accident against the odds (an English compromiser’s narrow defeat in the papal conclave in 1549), the Reformation might have happened without splitting the Church.

So far, so excellent. Despite refusing Freud’s help, MacCulloch is also good on Luther’s mind — his development and decline, the glories and glitches of his translation of the Bible, his equivocal relationship to humanism. The book deals critically but sympathetically with the contradictions of Protestantism — the reversion to reliance on tradition and authority, the sell-out to the state, the equivocations over freedom, the endurance of superstition and magic. The author has important pages, which everyone should read, on the compatibility of science and religion, and the humility of the pre- Copernican image of the universe.

There are moments of sheer pleasure — unforced flashes of wit and unforgettable stories, such as those of the “miracle of the Puritan mice” in Boston in 1640, or the wayward reformer in Strasbourg in 1527, who convinced himself that his mistress was the Virgin Mary. MacCulloch’s well-paced style makes the book seem half its length. His gift of clarity makes light of theology — the odium becomes intelligible, the tedium easy.

There are, however, some serious disappointments. MacCulloch ignores vast dimensions of the subject. He is uninterested in the geography of Protestantism: in the long run, in Europe, it was largely a peculiarity of lands around the North Sea and Baltic and a few rivers that drain into them. The most important current scholarship for Reformation studies is not on the arcana of theological and sexual deviancy, which MacCulloch masters perfectly, but on the trade and travel that unified the affected shores.

He also omits the global context. Comparison of the Reformation with similar movements in Islam and Buddhism at the time helps us see it for what it was: an effort of self-consciously godly elites to reform ordinary people’s lives by enhancing, sharpening and deepening their awareness of transcendence. He mentions that capitalism thrives in non-Protestant traditions, but never makes the killer comparisons with Buddhist, Muslim and Jain capitalism. He excludes Greek and Russian orthodoxy on the grounds that eastern Christendom never experienced a reformation. But in the true sense of the word, it did: here, too, neglected countryfolk and deracinated urban masses stirred clerical pride and conscience to new efforts of evangelisation. Today, confrontations of Catholic and Protestant mind-sets are happening, sometimes violently, in Latin America, which MacCulloch barely penetrates. Good as he is on sex (sexual liberation, he thinks, is only now undoing the Reformation ’s work), he never takes us beyond the bedroom into other spaces reformed by the clerical assault on popular culture — the sacred topographies of landscapes and cityscapes, the playhouses and fairgrounds, the salons of pious ladies, the redesigned church interiors, the seminary classrooms.

Like almost all writers on the Reformation, he ludicrously exaggerates its importance. He makes words falsely attributed to Luther — “Here I stand; I can do no other” — into “the motto of all western civilisation”. At the root of this improbable claim is an occupational hazard of scholarship. Like Christ in the desert, historians are self-exiled to the lonely wastelands of libraries and archives, where devils promise them the power to understand and even explain vast domains. But western civilisation is too vague and inconsistent to have a motto. Without the Reformation, modernity would still be modern. Magic would still have declined — and revived. The Enlightenment would still have challenged old regimes in thought and politics. Imperialism would have continued. Ideologies would still have excused war, oppression and genocide. And capitalism, science and technology would still have spattered the world with triumphs and trash.

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