To tell the people some rich family had been blessed by God to rule over them and pass that power down forever through their "royal bloodline".
In return, the Church received tribute from those rich families which it flaunted by coating the walls in gold.
The People revolted against the notion of being ruled over and demanded the right to select their own leaders but the structure of government still has traces of the old way which is why the highest elected office is Prime Minister. Think about that term.
No longer receiving a skim off the top of every country in Europe and with attendance in decline to where some churches are seen as nothing but architectural oddities, the Church found "true believers" to be fewer and fewer as people adopted reason and science over faith and mythology. This opened the door for people to enter the clergy who were in it for easy money or,...other motives.