During the time of the selling of indulgences, purgatory was (and still is, I believe) believed to be the midpoint between heaven and hell. God would send you there and you would have to spend time their for your sins you committed on Earth. The Catholic Church sold indulgences as a way of getting quick money. They told the people that buying indulgences would get you out of time in purgatory. The real reason the church sold indulgences was to get money to patronize art.