We studied the purgatory concept in history classes, covering a time when the Church had connected to strongly with the government.
The concept is taken from passages like 2 Maccabees 12, which is not part of the Protestant-approved Bible.
An interesing site that responds to the disagreement over purgatory:
http://www.cin.org/users/james/files/how2purg.htm, stating...
"the Catholic Church insists:
(1) that there is a purification after death,
(2) that this purification involves some kind of pain or discomfort, and
(3) that God assists those in this purification in response to the actions of the living. Among the things the Church does
not insist on are the ideas that purgatory is a place or that it takes time."
Some of the confusion comes from a relatively little amount written about afterlife in the Bible. There are quick references to sheol, hades, the grave, hell, heaven, the heavenly Jerusalem, and then beautiful descriptions of afterlife in Revelations.
Whenever we get the laws into our grasp, we tend to take on an air of authority that we know it all. I suspect that this is an area that God wants to keep us humbly reminded that He is in charge, and we are all subject to the same leveling at the end of our lives here.