One caveat: I'm an atheist, so I'm not speaking for anyone else specifically.
As far as I understand it, the Catholic church believes that you can be saved by works; that is, good deeds, living a good life, etc. While this prevents people like Gahndi from going to hell while Torquemada is in heaven, it also led to stuff like people being able to "buy" salvation by giving enough money to the church (considered a good deed).
Martin Luther broke from the church over stuff like this (the money thing, the idea that you have to go through a priest to talk to God, and more), and the Protestant church was born. Protestantism teaches that people can *only* be saved through faith, and works don't matter. That is, if you accept Christ as your savior, you're saved, and if you don't you're going to hell regardless of how good/decent/pious a life you led. That's it; any wiggling breaks from the teaching of the church.
To editorialize: I believe that the Protestant view is absolutely and completely monstrous; anything that rewards murderers (as long as they accept Christ) while condemning Gandhi and Einstein (among others), as far as I'm concerned has abandoned all sense of justice and fairness. It rewards ass-kissing and blind faith. I don't see one good thing about it. If it's true, the whole "Jesus died for my sins, isn't that wonderful" rings pretty hollow in light of the punishment I'm due for simply because I think with the brain God gave me. I make a reasoned and thorough decision based on what I feel is the genuine truth, and he's going to kick my ass forever for it? That's so just, loving, and compassionate! What a great God!
The Catholic view (specifically, "saved by works" doesn't seem so bad to me despite the past and potential abuses. It's somewhat more reasonable.
Well, at least I'll have some great company in the lake of fire, with the gnashing, and the screaming, and the hey hey hey.
-brennan