if every human is tainted with the guilt of the Original Sin of Adam, if Mary was not Immaculately conceived, then Christ would have the stain as well. how is He the spotless Lamb if He has that on Him? but then since Mary was free of that stain, then that does open the door for her to not die (since she never sinned and was not stained by Adam's sin), so there are some who believed that she never died.
Limbo happens when you have babies or pagans who never heard the gospel and were never baptized, so when they died, they still died guilty of Adam's sin. because of that, they cannot enter into heaven, but they did no evil (or were ignorant not of their fault), so they don't go to hell. hence, a third place where one grows in natural glory but not supernatural glory.
and the whole Calvin thing, if man is stained with that sin, it is not a leap to say he is totally depraved.
it's both. God sees (since He is outside of time) man's free will choices, and He elects or foreordains things to happen, people to call and when, etc. He does not, from before Creation, randomly pick who to save and who not to save. He knows who will follow Him.
