Season 5: Biblical stories are reenacted throughout this season, mainly, the story of Lucifer and Michael the Archangel. Sam and Dean are to represent them. Sam would be Lucifer and Dean would be Michael.
In real life, Jared Padalecki and Jensen Ackles are best friends and were each other's groomsmen. Jared Padalecki (Sam) and Jensen Ackles (Dean) have both said that they were skeptical at first about 'playing themselves'.