Purgatory to me is like a waiting area, where the spirits of departed people go after they die. Like being nominated for the Hall of Fame; Heaven or Hell, you wait in the crowd, until your name is chosen; first, second, or third round draft pick, etc.
The order of being chosen is connected not only to your own life, but also on the sentiment of the people you have left behind. They, through their love/hate and thoughts can add votes in your favor or disfavor; hall of fame or hall of shame.
Almost nobody is so perfect or so imperfect to go straight to heaven and hell. There is a pause for some extra data. This is why most people try to remember the departed, at wakes, funerals and memorial days, with good thoughts, in hopes that the departed can get closer to the front of the line. Some departed linger in line and are prayed for by the spiritual leaders in weekly services.