When the Forgotten Gods built the Mortal Realm in the Earliest Age, they made a place of joys and sorrows, freedom and labor. All the creatures of the land, sea, and sky worked for the many gods and enjoyed the spoils and trials of deities that had nothing but time and endless curiosity. These immortals could not fathom that the New Gods would one day rise and overthrow them in a violent battle, tossing them from their place in the high Hallows Above and entrapping them in the Mortal Realm and the Circles Below.
Many Forgotten Gods imprisoned in the Mortal Realm were trapped within the ground, buried over the centuries beneath the rise and fall of civilizations. The deific essence of these gods bleeds from their lasting wounds, seeping into the earth where they're entombed and running like veins of stone up to the surface. The crystal born from those veins is essentia.
Kudamat, the First Doom is one of them. In his triumph, the prophecy says, he will free the many trapped gods of his generation and become the high lord among all divinities.
Some in the Drylands follow the "forgotten ways" and use raw essentia in their spiritual practice.
Source · Drylands History