Trials of God

The Trials of God are a series of tests designed by God himself, in order to seal the gates of Hell or Heaven forever. According to Castiel, Sam's participation in the Trials of God, has affected him at a sub-atomic level.

The Trials to Seal Hell

 * 1. Kill a Hellhound and bathe in its blood. - Achieved by Sam Winchester, in "Trial and Error".
 * 2. Save an innocent soul from Hell. - Achieved by Sam Winchester, in "Taxi Driver".
 * 3. Cure a demon. - Almost completed by Sam in "Sacrifice".

Effects of the Demon Trials:
The demon trials create an extremely dangerous effect on the person as wherein the body and soul are converted and changed causing intense pain while their arms glow a white light. It was revealed in Sacrifice, that the person who completed the trials, would die. Though Sam stopped the trials before completely curing Crowley, the damage to his body was already fatal: all of his major organs were burned and it will take the angel Gadreel possessing him for an unknown period of time to heal the damage. After Gadreel was expelled by Sam, it was indicated the damage wasn't fully healed, but that it had healed to a point that Castiel over time could finish the job with his powers.