Random D&D grump: if your character concept involves the phrase “fanatical cultist”, the class you’re probably looking for is the cleric, not the warlock. You can totally play your warlock as a bargain basement cleric if you want to – it’s not like anyone can stop you! – but it can be a lot more interesting if you play up what most readily distinguishes the two archetypes.
In short, the warlock has an adversarial relationship with her patron. Being a cleric implies a certain level of devotion, or at least a level of shared goals between priest and deity, but a warlock doesn’t even have to respect her patron, let alone worship it. Their arrangement is a contract, and that contract allows the warlock to demand that her patron uphold its end of the bargain whether it wants to or not. A warlock can totally work against her own partron’s interests, then turn around and go “yeah, but I’m still technically in compliance with the terms of our pact, so fuck you, give me my spells”.
And as for the patron? Well, it puts up with the warlock’s bullshit because, as powerful as it is, it’s not actually a god: it needs mortal agents to work its will. And that usually works out for it, because it’s a billion years old and it knows a thing or two about pushing mortals around. There’s always that one prick who thinks she can game the system and win, though, and that’s the stuff that player characters are made of.
There’s lots of ways you can take that relationship; your warlock could be a conniving schemer, a smarmy kiss-ass, or anything in between – but if you’re not calling your patron by its first name behind its back, you’re missing out on your class’s full potential!
@adeptarcanist replied:
Oh, hm! Tbh I always like playing up the similarities between warlock and Paladin – the *contract* part.
Concept: a warlock and a paladin sworn to the same (Lawful Neutral) entity having theological debates about whether their patron is really a god.