It looks like they have loosely adapted the Dungeons & Dragons model of afterlife. In D&D (Forgotten Realms), the souls of the dead ended up in the Fugue Plane where they were judged by a deity who decided to which outerplane they were destined, according to their moral alignment. Then inhabitants of these planes will take them to their respective planes where they will become petitioners. More often than not, the petitioners lost all memories of their past lives and took the appearance of the denizens of their plane. A human worshipper of a dwarven deity will look like a dwarf. A petitioner of Mount Celestia will become a lantern archon, while a petitioner of the Nine Hells will start off in Avernus as a lowly lemure and then progress in the diabolical hierarchy.