The Roman Church had vast area of land stretching from one side of Europe to the other. From having all that land they had protection, wealth, an area that's good trading and importing, and a large population to support them.
The church such power that they could stop all nobles and kings to temporarily stop all war/battles for holy events or festivals. Citizens had spent almost all their life to religion and some chose the extreme life of a catholic monk.
The churches had monasteries that catholic monks lived in. The monks had spent most of their time recreating holy books. Those books were made with gold leaf paging and lots of colors to make them visible at the time of night.
The pope was even more powerful than kings. The pope could even excommunicate the kings and their kingdoms. Even though most of the kings were loyal some defied the rule of the pope and tried to take power from the church.
The church made it's money not by raiding land but having a tax for all faithful Christians to pay 10% of how much money they make. This had given the holy church plenty of money to build and gain more power, since almost all the people then were Christian.
The church had the lower people in the society help the people on top and the top helped the bottom. The church was ordered in a way that there was more people at the bottom to support the top.