the church of england started pushing this idea on people in the dark ages, it was a way to leech money off the populace. the story went that, if you payed the priests, then you would go to purgatory instead of hell, suffer moderatly for a while, then ascend. it's crap, from a crap organization. that is all.
EDIT: fine, i forgot the es, the CHURCHES of england, as in the churches IN england during the middle ages, and so i got my neurons misfiring about buying your way out of hell, i'll admit that that was wrong and accept the ridicule about that, but priests did accept money to pray and fast for people who wanted to bypass or at least lessen their time purgatory.