As the name suggests, the Church must have been the official religious body of D'ni (perhaps as opposed to sects and some independent prophets although their relationship is unclear) and led the worship of Yahvo. No doubt, its base must have been the Regeltovokum.
The body of the Church must have included priests and priestesses who officiated ceremonies like the marriage.
The 18th century was a time of fragile religious culture after the death of Ahlsendar. In 1779 Me'erta took the throne at the young age of 31, and many leaders, especially from the Church, publicly feared that his appointment would cause great damage. Indeed, during his time the cults fourished, the priests and prophets left to pursue other beliefs, and few remained in the Temple. This trend continued during the time of the Ahlsendar's Plague, where some D'ni expected "other gods" to save the people.
In the 24th century, King Naygen proposed the construction of a new Council Chamber for the Guilds, over the Tomb of the Great King. The official Church registered a complaint but very few opposed this decision.