An undercurrent running through all of this talk of Christianity and conversions is the two forces at work Christianizing the Island: Celtic and Roman.
Pope Gregory in 597 sent Augustine to Kent. Other famous missionaries like Paulinus followed in Augustine’s footsteps, teaching the Saxons of southeast England the wonders of Christianity. But this Christianity was according to Roman standards.
The Christians of the north were following a slightly different lead: They were Celtic Christians.
As has been examine before, the differences between the two doctrines may seem slight to us but they were massive in importance to the missionaries back then. The main difference was the method of calculating the date of Easter. (Again, it seems small; to the missionaries proselytizing the length of the Island way back then, it was a big deal.) Other differences were more subtle.
Yet differences they were. The Celts were more grounded in the teachings of Patrick and were more open to exploring the adoption of cultic gods and goddesses into the Christian family (like Patrick’s making Bride into St. Bridgit, for instance). The Romans, following Gregory’s lead, were more than happy to leave pagan temples standing but replace the pagan idols with Christian symbols. The idea of incorporating pagan gods or goddesses into the Christian pantheon would have given the Romans pause, however.
The point of all this is that the Christian movement was alive in well in Northumbria long before Paulinus arrived there in 627. The Christians in Northumbria were Celtic Christians, of course, Northumbria being much closer to Celtic lands than Kent. And when Paulinus arrived to oversee the marriage of Aethelburga to King Edwin of Northumbria, he brought his Roman Christian teachings with him.
Much is made of the very public baptism of Edwin and his “conversion.” Edwin and his people could very well have been practicing or at least discussing Christian practices already. Patrick, remember, was casting a long shadow across the Irish Sea long after his death.
Because Northumbria was the preeminent Saxon kingdom at this time, it was also the de facto battleground for the confrontation between Celtic and Roman Christianity. And matters came to a head in 654, at the Synod of Whitby.