The official religion of the Known Universe or the Corrino Empire was the belief system based on the Orange Catholic Bible, basically a concordance of the most important religions of the Old Empire which mainly contained elements from Navachristianity,Buddislam,Mahayana Christianity,Zensunni catholicism and the Maometh Saari religion.This religious beliefs were also known as "Orange Catholicism", "Koranjiyana Zenchristianity" or "Zenchristian Navislam."It's concept of God was a male-female-neuter trinity accepted as Supreme Being also interpreted as Buddallah or the Greatmother, the horned goddess and feminine principle of space.
There however does not seem to have been one single united orange catholic church, rather the different religious groups seem to have coexisted among the roof of orange catholicism.There also still existed minority groups of pre-orange catholic religions such as Judaism, as far as they were tolerated by orange catholic othodoxy.
The central teachings of orange catholicism were centered about the accord of Logic, reason,Galactophasic determinism and the doctrine of the Butlerian Jihad that "Man may not be replaced" and the ban of all Thinking Machines.Part of the power of the Padishah Emperor was that he guaranteed peace and safety throughout the empire and defended the orange catholic principles.The empire's ruling class itself however, including the Spacing Guild, was agnostic.
Fremen Religion was largely based on the Religion of the Wandering Zensunni, but had abandoned almost all traces of it's originally pacifist teachings.Fremen religion believed in surviving, fighting, strength and self-sacrifice for the tribe.Fremen religion also differed from traditional Zensufism through several folk-beliefs such as the reverence of the Sandworm of Arrakis (Shai-Hulud who could also appear as Shaitan) as a physical manifestation of God] and the impact of the spice orgies.
Fremen Religion had also been deeply manipulated by the Bene Gesserit through the Missionaria Protectiva and evidence that the first Sayyadinas of the fremen seem to have been rogue Reverend Mothers.Through this the Fremen-belief in a Mahdi had been strenghtened.
After the rise of Muad'Dib, Fremen religion turned to agressively converting and spreading their beliefs and became the dominant religion throughout the Atreides Empire until Leto Atreides II untimately replaced it with the cult of the God-Emperor.After Leto's death some splintergroups such as the Rakian Priesthood and variants of the Cult of Alia survived.
Little about the beliefs of the Sardaukar was known to outsiders, but as Salusa Secundus had been a station of the Wandering Zensunni's misr, it likely had a zensunnitic influence.The Dune Encyclopedia mentions the Tawrah Collegiate and the Torah and Talmudic Zabur of Salusa secundus so influences from Judaism also seem likely.It was widely acknowledged that the Sardaukar envisioned themselves as elite an superior beings.
Bene Gesserit Religion
The Bene Gesserit universally exploited the religious beliefs of humanity for their cause via the Missionaria Protectiva, were in one form or another seemingly active in the creation of orange catholicism, and held a body of quasi-religious principles and teachings, such as those preserved in the Azhar Book.Though their origins might have been in a pre-butlerian society or matriarchic cult and possibly some kind of goddess religion, the sisterhood, while officially posing as an Order of seeresses and councilors raising well-educated women, was in itself largely agnostic.It's prime concern were actually politics, and while they used religious language and teachings as a cover they really pursued the evolution of humanity, if under their tutelage, and for this sought to produce the Kwisatz Haderach.