Most Erfworlders believe in the Titans as Erf's creators or demiurges. Their divine will is used by Ansom, seeking to justify the traditional ruling systems of Erf, and by Stanley, who claims that the Titans have special plans for him that supersede the "mandate" of the royals, as evidenced by his attunement to the Arkenhammer. Images of the Titans are featured in the architecture of many cities; similarly, it would appear that some of the books popped along with cities make mention of the Titans.Erf-b1-p068
Some Erfworlders believe in an a City of Heroes, afterlife in which heroic deeds in combat are especially rewarded.
While no other deities have been mentioned, the Woodsy Elf warlord Tarfu invokes the blessings or guidance of "wood spirits" over troops before sending them into battle.Erf-b1-p057 This would suggest some animistic traits in the beliefs of this Elf brand.
Vinny also notes in First Intermission 37 that Signamancers subscribe to an esoteric philosophy which holds that all Stuff is Foolamancy, or, in Real World terms, that the physical world is an illusion, simply a set of Signs that represent an objects true nature. It is not clear whether this is truly a religious belief, a belief attached to the Signamancer's magical discipline, or simply a philosophical point of view.
It should be noted that, at present, there have been no unit types introduced in Erfworld that serve a primarily religious or priestly function. Casters appear to be the closest thing Erfworld has to a philosophical or priestly class, as they are most in tune with magic and spend much of their energy researching the arcane, as illustrated in Vinny's comments about Signamancers and Grand Abbie Janis's discussions with Sizemore throughout Book 1. However, while Casters have the free time and scholarly temperament to act as a priestly class, their subservient status to their Rulers makes it difficult to imagine how an organized religion could exist separate from a Sides power structure. So it is that, for much of the world, it appears that Rulers, and not individual units or organizations, set the religious policy and belief in their Sides. Thus, it is also the case that units with free-will like Rulers, Ruler-like units such as the leaders of Natural Sides and Barbarians, and to a lesser extent Warlords (which have some freewill, though it is tempered by their Loyalty to their Ruler and Side) are the ones that also debate the most about religious or philosophical issues.
A unit's religious beliefs are present when it is popped, though it may become more or less faithful depending on its experience.
Religious debates in Erfworld seem to take the form of the specific "plans" the Titans may have had for Erf and themselves: in other words, Fate. Indeed, talking about fate and destiny is likened to quoting scripture.