When a mortal creature dies its Soul goes to Purgatory to be cleansed. A place of spirit and shadow, Purgatory exists on a separate plane apart from Eden. No one knows quite how to enter or exit it, save for the usual way: dying.
The God of Death oversees Purgatory, helping clean the Souls that pass through. Once a Soul is properly cleansed, it can return to the source of all Souls, into the Light of Haven.