Gates of Oblivion
The Gates of Oblivion are a portal leading to many other planes of existence on the Great Moon in the Shadow World history. These are guarded by the Goddess of Death, Eissa (Lorminstra), who is the final arbiter in deciding the fate of souls. In the I.C.E. Age lore she would deny requests for lifegiving if the fallen had died in a significant or meaningful way, which is perhaps why the concept of deeds was necessary for GemStone III. Souls would be swept from the world to the moon by the River of Life, ending in the Spring of Youth, where they were cleansed of taint by implication from the Order of Vult (Voln). This is a natural phenomenon resulting from the flows of essence between Kulthea and Orhan. These are symbolically represented in the Order of Voln courtyard and The Graveyard.
In the archaic religion she would destroy souls that were hopelessly corrupted with her Staff of Doom, which was otherwise used to remove and insert souls as a fatal channeling. Such bodies are in comas, put into a deep sleep. The worst fate in her theology is for the soul to be destroyed, which is only possible when dealing with something associated with The Unlife. The Empress Kadaena is unrelated to this, her representation by Bandur Etrevion is idiosyncratic. The Staff of Doom plays into his use of Ordainer symbolism, and her necklace was a soul devourer even the gods feared.
The Keys to the Gates of Oblivion are carried by Eissa, with the keys of Life and Death opening the multitude of possible afterlives. There is a "forbidden" key which "must never be used", the Key to the Void, which were the demonic pales and so essentially hell dimensions. In the early Shadow World lore the nature of Oblivion was left vague. The death mechanics of GemStone III had its own special place called Purgatory, which represented the other side of the Gates of Oblivion. It was a limbo where souls waited to choose their eternal fate in a dream state, with paths of light and darkness, which arguably reflects "the dark path" and the possibility of being "lost to the demonic" literally. The Dark Lords of Charon (Lornon) would, in contrast, send the souls of their followers to the Pales.
Behind The Scenes
The "Gates of Oblivion" are now called "the Ebon Gate" in the modern history of Elanthia. It is no longer possible for player characters to be "lost to the demonic", and the other side of the gates is sometimes called Eternity. Some adventurers visited what could have been the moon at the end of the first Griffin Sword War, making use of Lorminstra's "Lake of Tears", which is not Shadow World canonical and later referred to Mount Aenatumgana. However, the pool it initially grew out of was probably the "mere" pond by the Spring of Youth, through which Eissa watched her followers. ("Eissa's tears" were special gemstones that warded off evil, but there was no theological explanation.) The premise was that Lorminstra shed a tear for every soul that had chosen the path of darkness, and every life that had ended unfulfilled or prematurely in an insignificant way. This was an important aspect of her archaic theology which is not represented modernly but still was in the Griffin Sword War.
The death mechanics of Purgatory represented "Oblivion" as a timeless void suffused with hopelessness and doom, where all memory and sense of identity of the material world washed away into nothingness. This was GemStone III specific and relevant to the symbolism of The Graveyard. The prophet of the first Griffin Sword War turned out to be Morfell himself, who originally sundered the sword tainting it, who had his identity and memory taken away by Lorminstra until redeeming himself. There is the additional nuance that the moon of the dark gods was named after the mythological ferryman of Hell. However, this stems from the Shadow World source material itself, not GemStone III itself. The relationship of the Dark Lords to the symbolism in The Graveyard is far more subtle than Eissa and the Gates of Oblivion. It was more overtly elaborated in The Broken Lands, with its relation of the dark gods to the Lords of Essaence, which should be regarded as a spin-off of the same story.
Lough Ne'halin in the Lysierian Hills seemingly translates as "lake without salt", and apparently alludes to the Lake of Tears and its relation to purgatory. Various aspects of the first Griffin Sword War story correspond to Holy Grail story variants, where the weeping young maiden (Lorminstra) is the Grail bearer, and the Griffin Sword corresponding to the sapphire hilted Grail Sword which breaks into pieces. There is a Germanic variant of the story, particularly Wolfram von Eschenbach's Parzival which was used in the loresong of Terate's void blade, where it has to be reforged by putting its pieces into a lake and thus a "sunsword." The trope of a hero not knowing his own name is common to the Perceval variants, and the guardian of the lake asked its purpose, which is a common motif for holy relics in the stories. The swelling of a pond into a lake of tears might be an Alice in Wonderland reference, with possibly others implied in Castle Anwyn, with the serpent mirror as the analog of Eissa's "mere."