The planet Earth is made up of one giant supercontinent that all of humanity live on. The landmasses are separated by jungles, deserts, mountain ranges, large rivers, and other geographical barriers. However, They are all connected through portals called Realm Gates, which are scattered thoughout the supercontinent. The portals vary in size, from those which could only transport several people at once, to larger ones that can move hundreds or even thousands. These gates exist across different different countires. Their people have their own cultures, traditions, and celebrations, but all follow one organized faith.
Realm Gates are controlled by the organized religion, which exists in some form across these countries on the continent. Priests are the only ones who can activate or de-activate the portals. Churches spring up around these gates, and control access to them. They are considered sacred gifts from the gods, and destroying one is considered sacrilege. The knowledge of these portals are known to the public. These gates connect to each other as well as to the Main realmgates at the country's capital. This gate controls all the other gates in the country, and connects to the realmgates of the capitals of other nations.
The world exists alongside a parallel reality that is equivalent to hell. This realm is filled with creatures called daemons that cross over into the world. The only thing keeping the daemons out is a thin barrier that exists between realms. This barrier is powered by human worship. Because of this, The religion wants to maintain a unified church without splitting into different factions like the monotheistic faiths of today, such as christianity and its many denominations. Since there are numerous countries on the landmass, each with its own people and cultures, it would be difficult to keep the faith consistent without causing misinterpretations and unwanted additions.
How can I credibly describe how this church maintains its unity across a supercontinent without splintering?