After a mortal dies, its soul is said to be escorted from the mortal realm by Mortus to Lethe, the river of forgetfulness and the Stygian Marsh of Limbo.
Souls accumulate enegies during their mortal life based on the nature of his deeds.
The souls who are judged to be wicked are sent up the river Cocytus to Cania where they congeal into lemures and can eventually become more powerful devils, or the river Phlegethon to Infernus where they are used as materials in the Blood War between Devils and Demons of the Abyss.
Those that are of an evil too powerful to be given to the devils of those realms are sent along the river Acheron to be imprisoned in Tartarus for all eternity.
Souls that are judged to be neither good, nor wicked are of no use to the axiomatic forces and are set free to wander Limbo until they eventually become one with the plane.
Good souls are collected by astral devas and taken to the celestial peak where their essence can be used to sustain the celestials in a similar manner as food to a mortal.
Pure souls, such as those of saints or other scions of good are often escorted to the celestial realms after death and continue their existence without tasting Lethe, the river of forgetfulness. Here they retain their forms and can eventually become celestials themselves.