National Geographic is reporting on a new study that claims the Normans introduced the idea of demonic possession to England in 1066. Professor Peter Dendle of Penn State says that "there is no reference to a contemporary Anglo-Saxon case of possession for 300 years" prior to the Norman Conquest:
Anglo-Saxon sources indicate that the English were both puzzled and surprised by cases of possession mentioned both in the Scriptures and European texts from regions such as modern-day France and Germany.
But after the Norman Conquest, possession stories and exorcisms quickly appear in England, Dendle found.
These reports coincided with growing use of healing shrines and pilgrimage routes by people in search of miracle cures, the researcher suggests.
Christina Lee of the University of Nottingham in England says saintly relics that supposedly had healing properties were increasingly advertised by monasteries and churches as cures for the possessed or the mad.
"There were churches vying to have the most powerful saint, while monasteries had hospitals attached to them," Lee said. "They saw themselves as doctors of the soul."
One argument is that demon possession as a religious concept was good for business.*
If cures appeared to work, "people would be very grateful and leave donations—which the churches and monasteries were dependent on," Lee pointed out.
The illustration is a 1598 woodcut showing an exorcism from Pierre Boaistuau, et al., Histoires prodigieuses et memorables, extraictes de plusieurs fameux autheurs, Grecs, & Latins, prophanes (Paris, 1598), vol. 1. Reproduced in "The Devil in the Convent" by Moshe Sluhovsky.
*Although I haven't read the original argument, this seems to be a pretty facile answer to me. I think cultural and political influences would have been a much stronger motivator than purely economic ones.