Medieval texts that recorded everything happening at the time. Most of our written records from the medieval period come because the monks wrote these. The monks also made copies of ancient texts which is why we have them now too.
The Christians that protested against the Pope and the Catholic Church. While they were still Christian, they had their own beliefs about Christianity that was more focused on getting into heaven based on receiving God's grace rather then good deeds.
All Catholic bibles were written in latin in the Medieval period and the clergy could read latin, and the clergy did not think that the average person should need to read the bible as they could follow the teachings of their priest and the Pope.
The isolated churches just for monks. Henry VIII made a deliberate effort to abolish these when he broke with Rome. He took a lot of their wealth when he did.