The story of three thousand years of a faith which spread across the entire globe, splitting into numerous fragments each conditioned by entirely different social and political circumstances, is a daunting challenge for both the author and the reader. Perhaps the greatest compliment that can be paid to Diarmaid MacCulloch is to say that, after over a thousand pages, one is left longing for more. With elegance, dexterity and lightness of touch he winds his way through movements of infinite complexity, clarifying, often with a single comment, polemics which have puzzled theologians through the ages, passing with ease and authority from country to country and from period to period, and dealing knowledgeably with the architectural, artistic and musical innovations that attended the spread of Christianity.

MacCulloch's object is to demonstrate the ‘extraordinary diversity’ that characterises the Christian faith, the countless combinations resulting from its ‘twofold ancestry’, a descent from both Greece and Israel. MacCulloch deserves special praise for his sections on the Russian and Greek Churches and above all on eastern communities such as the Church of the East and the Church of Ethiopia. Where Europe is concerned he assesses most of the movements that have been marginalised or condemned by the main Churches. In accordance with recent research in Italy, Juan de Valdés and his followers, the spirituali, are given their due – indeed, future generations of historians might judge that they get even more than their due. MacCulloch is also sensitive to the somewhat paradoxical interaction of apparently conflicting creeds. He reminds us that the Enlightenment was far more indebted to Christianity than has often been acknowledged, that the nineteenth century, all too frequently associated with Feuerbacher, Darwin and Marx, and regarded as ‘a century of disenchantment with Christanity and the supernatural in an age of science, a period of ebbing of European faith’, was in fact ‘crowded with visionaries both Catholic and Protestant, full of excitement about the End Times, noisy with the sound of building for new churches and monasteries and the voices of furious quarrels about the best way forward for Christian renewal’. He also brings out the many points of community of the sober Catholicism of the Counter-Reformation and the strict moral aims of the Protestants.

A book as long as this, on a subject of such immense breadth, inevitably incurs the danger of an occasional oversimplification or omission. In most cases one would simply like to have more – a little more, for example, than a single passing reference to Lorenzo Valla (who has not made it into the index) in a discussion of humanism and Biblical scholarship. But more could certainly have been said about the genesis of the Vulgate, since the reader is now left with the impression that Jerome translated the entire Bible rather than frequently building on, or adopting, earlier translations. To say, in a discussion of the fate of the Spanish conversos and the estatutos de limpieza de sangre, that ‘few of the higher Spanish nobility could claim such purity of blood’ is correct, but Spaniards with a patent of nobility, which counted for infinitely more than a proof of racial purity, would be most surprised to read that ‘they found themselves excluded from high office in the Church in favour of social inferiors who could prove their lack of taint’.

One of the most interesting sections is the discussion of Erasmus. MacCulloch emphasises Erasmus' profound debt to Origen, but he also presents him as a dyed in the wool radical. Many radicals, certainly, would have agreed. They used Erasmus as if he was one of themselves. But Erasmus' own horrified reaction (in a letter to Bucer) to his treatment by Sebastian Franck, who hailed him as an enlightened heretic after his own heart, shows how little he himself accepted this view. Erasmus did indeed ‘pour scorn on the so-called “Johannine comma”’, but MacCulloch does not add that, after originally omitting it from his Novum Testamentum, he reinserted it in the third edition.

‘My aim’, writes MacCulloch, ‘has been to seek out what I see as the good in the varied forms of the Christian faith, while pointing clearly to what I think is foolish and dangerous in them. Religious belief can be very close to madness. It has brought human beings to acts of criminal folly as well as to the highest achievements of goodness, creativity and generosity.’ A History of Christianity ends with the question of the future of Christianity. Should we be optimistic or pessimistic about its survival? The statistics inspire hope. In 2009, MacCulloch tells us, Christianity had more than two billion adherents, ‘almost four times its numbers in 1900, a third of the world's population, and more than half a billion more than its nearest rival Islam.’ But, he adds, ‘Christian history offers plenty of sobering messages for overconfidence.’ Certainly, if we judge by the policy of the leaders of the Churches, there is less cause for exultation. MacCulloch is particularly critical of Paul vi's pronouncements against birth control and of the crudely unaesthetic results of Vatican II – ‘a multitude of tables often cheap in appearance if not in cost camped out in historic church buildings, while the emphasis on celebrating congregational Masses at a single main altar left the greater galaxy of side altars dusty and neglected’. Nor are the Protestant, or even the Orthodox, worlds much better. MacCulloch reminds us of the views expressed by American Evangelicals under the presidency of George W. Bush – of James Inhofe's assurance before the Senate ‘that Al Qaeda's destruction of New York's World Trade Center in 2001 was divine punishment for the inadequacy of America's support for Israel’ and that global warming was ‘the greatest hoax ever perpetrated on the American people’. Statements such as these, so much at odds with the humane faith with which MacCulloch clearly sympathises, justify the desire that a Christianity which can lead to ‘acts of criminal folly’ may be replaced by something better.