Bernard Cromwell has a new book, The Pagan Lord, which is set in 9th century Britain. The book is about the making of England and how Christianity spread in the region. The Historical Novel Society had an interview with Cromwell on this book and in this answer he explains why Christianity was easily embraced by the Pagan cultures.
TLL: There are strong themes of religious tug-o-war in your Saxon books. What are your personal thoughts on why Christianity was so easily embraced by Pagan cultures in Britain? Why did a people whose spirituality was so connected to the land and the elements give up that connection (and protection) for this ‘new’ God?
BC: I’m not sure the process was that easy, and pagan superstitions lingered on for centuries. In almost every case the conversion was top down; the missionaries converted the ruler and he forced it on his people. I suppose the crucial difference is that Christianity offered an afterlife. So, of course, did the religion of Odin and Thor, but that afterlife was really only for the warrior class while Christianity’s heaven was for everyone and that had a much greater appeal to women, and women are the real transmitters of culture (they raise the infants). The pagan religions tend to be very male oriented. Then there’s the exclusivity of Christianity; it doesn’t tolerate other religions. Most pagan religions were tolerant; they accepted that there were many gods and goddesses and didn’t persecute people for believing in those other deities, but Christianity wouldn’t abide competition and was savage in its intolerance. Religion, at heart, is simply an attempt to answer the unanswerable questions (why did the harvest fail, why did my child die, why why why?) and paganism tended to fatalism (it just happened, live with it), but Christianity offered the solace of recompense; your child might have died, but you’ll be reunited in the afterlife.[Bernard Cornwell on Pagan Lord, Uhtred’s latest blood-drenched outing]