The Hierocracy had been a time when the Vorin Church attempted to rule on Roshar politically rather than merely acting as spiritual guides. The Church tried to conquer the world and control the people "for their own good." Priests controlled what people learned, what religious paths they followed, and the overall doctrine, because they claimed that the common people could not understand theology. They justified this with visions and prophesy they claimed to see.
”They were taught to follow the priests. Not the Almighty or the Heralds, but the priests.— Kadash 
In the present day the Hierocracy was considered the failure of Vorinism.