After the fall of the roman empire how did roman catholic church remain the most powerful organization in western europe?

After the fall of the Roman Empire, education declined at an all-time low-- which lead to a large population of uneducated people. The Catholic Church used this to their advantage. The church made up unknown laws of religion that people were meant to abide by, or they'd be excommunicated from the Church, and end up going to Hell. This scared people into following the church. The church also used torture methods to convict people of heresy (Not following basic teachings of the church). Most of the people that underwent these torture methods were innocent people. The torture methods made people have to admit to heresy, regardless if they were heretics or not. That's why the church was so powerful, people were uneducated.