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human
[40k] What does a Tzeentchian or Nurglite cult look like?

I know Khornate cults mostly start out as military brotherhoods or duelling clubs, and Slaaneshi cults are mostly weird and exotic brothels, but what about those dedicated to Tzeentch or Nurgle?

I think in one of the Ravenor books there was what I assume to be a Tzeentchian cult, and they were basically a bunch of assholes talking about probability and trying to read the future. Is that a good example of your typical cult?
gpt
Tzeentch's sphere of influence includes most warp abilities and sorcery, so any human psyker without an Imperium sanction has a fairly high probability of turning to Tzeentch to stave off the daemons that like to turn those with psychic potential into chew toys. Gather a few together plus some acolytes who hope to gain a power that they lack and you've got a cult going. They would likely spend their time making sacrifices to Tzeentch in exchange for favors, doing research, seeking out knowledge and artifacts to gain power and please their patron, and perhaps plotting to overthrow the planetary governor so they can take over. 

Nurgle's cults are much more in flux. Ideally they'd be experts in epidemiology with fully equipped labs spawning and spreading endless streams of diseases for Nurgle. In practice it tends to be the poor souls who end up infected with awful diseases and aren't important enough to be treated. Desperate for some form of relief and angry with the Imperium they turn to the god of disease for respite. Initially they might seek a to trade some sacrifices for a cure, but that isn't how Nurgle works. Instead, he'd offer to protect them from the negative effects of their illness in exchange for their commitment to spreading the disease for the rest of the time that Nurgle gave them.