Why was the church in medieval europe such a powerful influence on people's lives?

Because people basically had nothing so they turned to the church and God for help

The people of the church themselves believed they had divine right (belief that god had chosen them and whatever they said was right) so people followed. the intelligence of the medieval people was low since almost no one was literate so the only people who knew how to read were usually those in the church. most of the population followed blindly since they didn't know any better, without the renaissance and enlightenment eras.