In this world there is only one pantheon of gods. They are human in form, and exist in another dimension connected to the material plane. One god sits at the top and rules over all creation, with the other gods being subservient to him. They spend their days making sure everything in reality funotions the way it should (sun rises and sets, gravity and physics work, etc). They also must defend the material plane from things that exist outside of reality, such as eldritch abominations. They are in a constant war defending creation from these monsters.
All nations are aware of the ongoing war, and that gods are real. Since they keep busy fighting for humans, it is difficult for the gods to find the time to run the day to day tasks of world empires, and they rarely visit the realm. It is very rare for people to meet the gods. Instead, they select their most devoted followers to rule in their stead. These followers communicate with their gods directly, and rule with their authority. Nevertheless, there are different empires with their own unique cultures. Every religion is based in some form of the original faith.
How is it possible that religious diversity and culture could exist in a world where the gods are active?