Almost always when an institution or group claims to have authority from God, the primary enforcement tool used to establish control over others is fear. Authority from God relieves the claimant to the authority of any need to display merit apart from the claim of authority itself. The Catholics were able to engage in excesses, abuses, even outright institutional evil, but these great wrongs were regarded as unimportant because of the claim to have authority from God.
God's holiness was embodied in "keys" given from Peter. They were thought to allow holders of the authority to seal in heaven. This silenced the critics. The fear of being kept from heaven or consigned to hell was enough to rule over the souls of men. They could claim they acted from a higher plane, with God's ways remaining mysterious, even incomprehensible to the common man. The power of God can judge others, but no may can judge God under this system.
If mental coercion did not work, then credulous and cruel believers could be employed to intimidate and get control. If more was needed, the Catholic hierarchy felt no inhibition at using violence to be able to rule and reign over the souls of men.
The Pope did not need to display virtue, only power. He did not need to produce revelation or expound on how men could entertain angels, only to appear in the seat of power, displaying the incidents of authority, wealth, privilege, standing above the common man in a place filled with art, treasure, statuary surrounded by supporters. These trappings were a substitute for revelation and authentic fruits from heaven.
This formula worked to keep all of Christendom subordinate to the rule of oftentimes wicked, even cruel, men. For nearly a thousand years it monopolized power over men. Because these pontiffs claimed to hold God's authority, people feared them and were loathe to challenge them. When the bedrock of an institution's claims rests on authority, these failings are almost always eventually unavoidable. God's power is so resilient, so powerful, so vital for salvation that almost all men will surrender to it or be forced to submit when a group trusts that it exists.
These are powerful forces. When released upon the stage of history, they are meant to be held by only the meek, the humble, and the servants of all. Never by the proud, the vain, and the ambitious. But it is always the proud, the vain and the ambitious who are drawn to seek to hold such authority. Hence the many sycophants who always congregate at Rome.
We see some of this very excess on display within radical Islam today. Brutality is justified by God's power; God's right to kill. No one questions God's right in such matters. But what man is there who can be certain of God's will until he has stood in His presence and learned how great a gulf exists between the foolishness of man and the holiness of God? But those are rare indeed. It is far easier to claim to speak FOR God than to actually speak WITH God. Whole cable networks are filled with clamoring clergy claiming to speak for Him. They'll be the first to burn, because the command to not take the Lord's name in vain is, after all, one of the Ten Commandments.
History is the stuff from which most clearly the warnings of scripture take form in flesh and blood. All the warnings are there, but we frequently believe them only applicable to those we know to have fallen. But the lessons were always meant for us. ...