That's a bit of a misnomer - Britain was Christianised largely peacefully, with the exception of the Synod of Whitman where Roman Christianity was enforced on the Gaelic missionaries.
They were not the ultimate shelter, they were virtually the only shelter - until the secularisation of the universities Higher Learning was the preserve of the Church, and outside the more isolated places like Ireland (and Wessex England), and a few brief epochs like the rule of Charlemagne, secular lords were not interested in learning letters. Private book ownership was not common even among the gentry until the High Middle Ages.
The Roman Church was the only part of Roman society that was able to endure, by offering the barbarian lords sanction and a way to organise their large new holdings effectively.
You mentioned the Vikings - in France and Ialy they Romanised, and in Britain they Anglisised - which included their leaders adopting Christianity, building Churches and Monasteries and having clerical tutors for their children. They really wanted to be Roman, everyone did, and the Church was able to do that for them.
Hell - look how Roman we are. We're having a Roman debate, writing Roman script, using a language which is part-Latin...
All because of the Church - the script is even based on the one used by Charlemagne's monks!
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