I'm a wee bit curious, Alan.
Would this 'devil's work' in the Middle Ages and rennaisance really hold up?
Why would God, if He thought the RC church was a great example of faith, allow venial, corrupt men to claim to be Christ's vicar on earth - whatever that means?
Why would He allow generations of Europeans to suffer and labour to finance this veniality in what was supposed to be His Holy City?
Why would He allow the abhorrance of the Conquistadores, Inquisition, etc?
Or was God really preparing the way for Luther?
You see, just attributing the corruption to the devil is a bit of a cop out.
In reality, the Western Church, modelled as it was on the civil structures of Imperial Rome, became subject to all the flaws and opportunities inherant in that very system.
That system was not some divine ordination; simply the result of a very pragmatic Constantinian interferance with church governance, centralising power with all the possibilities of misuse of that power.