You might call it the ultimate theological rags-to-riches story: how a socially insignificant young woman from a backwater of the Roman Empire became one of the three or four most instantly recognisable religious images in the world. Exactly how this happened is a fascinating story. Somehow, the mother of Jesus came to be employed as a means of making sense of an exceptional range of human experience – not only virginity but motherhood and family life, not only poverty and humility but the world of power and patronage, not only the triumphant celebration of God's epiphany in flesh and blood but also that distinctive kind of suffering that is blind helplessness in the face of the suffering of someone you love.

The strength of this book by Miri Rubin, one of the most interesting and original of British medieval historians, is that it charts the ways in which Mary is "used to think with". Perhaps its most dismaying pages are those that deal with how Mary's identity became a way of framing Jewish-Christian debate. Mary is unmistakeably Jewish – indeed, for some Christians, archetypally Jewish; she is the exemplary Jewish person, the one who does what God meant the Jewish people to do. It makes sense that she is specially concerned for her own kin. But, in legend after legend, that concern is shown chiefly in procuring conversions, often after threats and violence.

It is not surprising that medieval Jewish polemicists hit back with abusive and defamatory representations of Mary. And Rubin is right to note the radical difference in this respect between Jewish and Muslim attitudes to Mary: the Koran has more about Mary than the Bible does, and Islamic tradition is often extravagant in her praise. Nothing is really at stake here between Christians and Muslims; but the Jewish-Christian debate in the Middle Ages is another matter. For at least some Jewish writers reacting to Christian triumphalism, Mary is something of a symbol of infidelity to her people – a metaphorical as well as literal adulteress. There is room for a whole book on this subject and Rubin is uniquely equipped to write it.

Sadly, this particular book suffers from poor editing. There are repetitions (at least once an artefact is described twice, independently, within a very few pages), confusions in the ordering of material (several references to the familiar legend of Mary's rescue of the Faustian cleric, Theophilus, before the story is actually told), and a general impression of arbitrariness in the selection of some material. It is not clear, for example, why the section on Mary in Burgundy should be followed immediately by one on Mary in Ethiopia, given that we have had nothing on Mary in the eastern churches for several chapters. True, both deal with Mary as patroness and anchor of a royal ideology but these pages sit oddly in the middle of a resolutely European discussion. The western medieval material is clearly where the weight of the author's interest lies, and all of it is intriguing and significant – but it is not easy to keep one's bearings, chronologically or culturally, in these sections.

Sometimes in a capacious and vastly learned book the reader senses a tighter argument trying to break through, which might have made a shorter and better focused work. And this is true here not only in the treatment of the medieval material but in the organisation of the whole book. The attempt to produce a history of the perceptions of Mary from their beginnings to the 21st century means that the sections on the (mostly western) Middle Ages are flanked by discussion of early Christian texts and images and by some treatment of the Marian cult in the modern era (including its developments outside historic Christendom, in Asia and southern America for instance). The early Christian sections have an uncomfortable number of plain errors – including a certain confusion between Greek-speaking West Syrian literature and the works written further east in the Syriac language, two worlds as different as Sunni and Shia Islam in their theological and devotional assumptions.

As for the treatment of Mary in the post-Reformation world and the modern era, it reads rather perfunctorily. Rubin touches very briefly on the complex politics (national, linguistic, class, gender) around the many apparitions of Mary in the 19th century and after but she mentions only a couple of these – and her description of Mary's injunctions to Bernadette at Lourdes ("to promote a new heavenly order of purity") bears little relation to the straightforward emphasis on repentance and healing relayed by Bernadette herself. There is a mention of Pope John Paul II's enthusiasm for the cult of Our Lady of Guadalupe, the hugely popular miraculous image from 16th-century Mexico, but nothing on the vastly important role played by Mary in the whole of the late Pope's theology and spirituality – not to mention the political weight in Poland, especially in the 20th century, of devotion to Our Lady of Czestochowa and her title as Queen of Poland.

In short, Mother of God is a treasury of raw material but doesn't quite add up as a single work. In the last few chapters especially, the reader has a feeling of research that has been a bit rushed in order to touch as many bases as possible. This would have been a more satisfying book if it had concentrated on the Middle Ages and avoided the earlier and later eras. On these subjects, there are, as Rubin's excellent and copious references make plain, better and fuller studies.

But what it does is implicitly alert us to the basic fact about the cult of Mary that has made it such a resourceful set of images for understanding all kinds of cultural identities.

Mary is an embodiment of paradox: she is the one whose human freedom sets free the action of God in the world – and at the same time the one whose response to God is already foreseen and enabled by God as the means of exercising his freedom. It is a vertiginous set of claims but at its heart is the recognition that human freedom and divine freedom cannot be understood in abstraction from one other. And, in a climate of scepticism and confusion about both sorts of liberty, that recognition remains a cultural and imaginative challenge of unique seriousness.

Copyright The Financial Times Limited 2009