The Obliviati
In the centuries since the Heralds of God in Heaven first came to the Prophets with their message of salvation, many entities from Beyond have styled themselves as Heralds, seeking to lead the faithful astray. One of the most successful of these impostors is known as Nox, the patron of the cult called the Obliviati.
Into the Pits
The Obliviati promise secret knowledge to those who join their ranks and have gathered many converts over the centuries. Initiates are placed naked into muddy pits and instructed to squirm into the earth, seeking a hidden place beneath the soil where they might encounter Nox. They spend years - or even centuries - underground, sustained by the power of the eldritch outsider, while their minds and bodies are reshaped for its purposes. According to Obliviati lore, it is during this period that the convert attains the secret knowledge they were promised - truths granted only to those who have fully embraced darkness and shadow. These seekers are known as worms; the Obliviati honor worms as natural seekers of darkness and truth, and many adorn themselves with worm motifs after they emerge.
What crawls from the dark soil after this period of transformation is barely recognizable as human. Pale and elongated, their bodies have become wormlike, and their minds strange and warped. Only by wrapping themselves thoroughly in clothing to conceal their form and wormlike faces can they hope to pass through human society unnoticed - and even then, they are seen as odd, both in gait and in the ever-present smell of wet earth. They congregate in underground places and emerge aboveground only at night, usually when rain is falling.
Disinterring Memory
Their time beneath the earth also grants them a peculiar power: the ability to unearth horrors hidden within the memories of others. The Obliviati lure their victims with the promise of answers, then recount tales of the victim's own past - horrible incidents that become real in the listener's memory as the worm-men speak them. These stories are carefully crafted to sever the bonds that tie the victim to the surface world, destroying friendships and fracturing family ties by inventing crimes committed by or against the targeted soul. The Obliviati always claim to be helping the individual see the truth - but the "truth" is invariably that the victim has been horribly wronged by those they once believed loved them. Some see through these tales, despite the uncanny sense that they are their own memories, but most are convinced that their life up to this point has been a lie, and that the truth lies buried deep within.
These stories are often accompanied by suggestions that the victim is special in some way - that they may be capable of reaching truths unavailable to others if they journey to Nox, the Herald Beneath. According to the Obliviati, when someone holds a falsehood about themselves as truth, they separate themselves from Heaven; only those who have discovered the real truth can hope to attain salvation. The cult emphasizes that there is always a deeper truth buried beneath those already known - truth is portrayed as a vast and shadowed object, perceptible only to the diligent. Light, they claim, serves only to distract from this truth; it is the very stuff of illusion and must be shut out so that the hidden reality can be revealed.
Taken together, this creed draws the curious to the Obliviati. The memories revealed by the worm-men sever their ties with the surface folk, while the promise of wisdom and salvation pulls them ever deeper into the pits beneath the earth. Initiates spend increasing amounts of time in caves and sewers, adopting nocturnal habits and breaking any remaining connections to those who dwell in sunlight. Occasionally, they attempt to bring loved ones below with them - but such efforts rarely succeed. Ultimately, unless prevented, the initiates of the Obliviati descend into a shadowed, muddy pit, pressing their faces into the soil as they writhe and squirm their way underground.
To What End?
The Obliviati appear to exist solely to recruit others into their order. They do not enact other plots, nor perform rituals intended to summon their patron into the world - a procedure they insist is unnecessary, for Nox already dwells beneath the earth. When asked why they pursue converts with such diligence, they claim it is their duty to save as many souls as possible - and that the only path to salvation lies through the shadows.

Why'd it have to be worms? LOL! Take out the worm part and this isn't so different from real world religions.
I may have taken inspiration from a few historical moral crusades.