Supernatural S04 E02 Are You There, God? It's Me, Dean Winchester

"Saving people, hunting things, the family business."

After Dean's encounter with Castiel, Dean, Sam and Bobby brush up on their biblical lore when they're attacked by the vengeful spirits of people from the Winchesters' past. They're warned it's a sign that someone is trying to break seals which will bring on the apocalypse.