No one who witnessed the recent ceremony to beatify the late Pope John Paul II - when his exhumed coffin lay before the altar of St Peter's, while a vial of his blood was displayed in an elaborate silver reliquary for veneration - could miss the centrality of what Caroline Walker Bynum calls "holy matter" in Catholic religious practice. As she points out, this persistent and pervasive Christian concern with "materiality" was at its most intense in Western Europe in the later Middle Ages, the period from the 12th century to the early 16th that forms the subject of her profoundly absorbing book.
For some readers, the mention of medieval relics will summon up the spirit of Monty Python, and those looking for anecdotes to rival the Holy Hand Grenade of Antioch will not be disappointed. There are the hairs of the 13th-century holy woman Mary of Oignies, preserved separately from her body, which came alive for an hour to cure the sick, and the foot of Agnes of Montepulciano, which rose from her bier to salute a visit from the 14th-century saint Catherine of Siena, not to mention a 15th-century prayer for the blessing and exorcism of radishes.
It's all too easy for 21st-century eyes to see nothing here but credulity and superstition, but Walker Bynum's remarkable achievement is to reveal how alive with meaning were these experiences and the theology that sought to explain them. This is one of those rare books that can make one look at the world in a new way.
It should come as no surprise, perhaps, that a religion founded on the premise that God was made flesh should be preoccupied with physicality. But the nature of that preoccupation, in Walker Bynum's account, challenges some of our most deeply held assumptions. We draw fundamental categorical distinctions between living and dead, animate and non-animate matter. But in the medieval mind the essential boundary lay instead between materiality and transcendence - between a physical world where matter of every kind was liable to change (whether generative or degenerative) and the eternal immutability of heaven.
And in a world where all matter has the potential to undergo processes of birth, metamorphosis and decay, the sudden animation of a dead saint's hair or foot becomes much less surprising - although no less challenging in the anxiety such miraculous moments of material change provoked about the nature of their relationship to the divine. The same anxieties and enthusiasms were also raised by the religious art of the Middle Ages, which, as Walker Bynum demonstrates, is much less concerned with "realistic" visual representation than it is with the actual physicality of both its materials and its images.
In fact, there might be no distinction between these ostensibly different categories of holy objects, given that paintings and sculptures often contained relics - or became them, if they miraculously bled, sweated, spoke or moved. "One might say", Walker Bynum wryly remarks, "that to a modern theorist, the problem is to explain how things 'talk'; to a medieval theorist, it was to get them to shut up."
For all the discussion of "thingness" and "stuffness", this text demands concentration (and possibly a dictionary for anyone whose vocabulary doesn't normally extend to "theurgic", "somatic" or "apotropaic" - although the author does offer a definition of the prayed-for radishes). But it is well worth the effort: an extraordinary, moving and thought-provoking evocation of late medieval devotion in all its contradictions, paradoxes and multiplicities.
Christian Materiality: An Essay on Religion in Late Medieval Europe
By Caroline Walker Bynum. Zone Books, 408pp, £22.95. ISBN 9781935408109. Published 10 June 2011