Instead of looking to the extremely fractured religion of Christianity, as it implied by your use of the word "church", look instead to Hinduism.

In our world, in Hinduism, there is almost no centralization, and a huge variation in dogma and in what is considered scripture. There is even more variation in what how scripture is interpreted, and a millions times more variation in ritual and religious practices. And this is in South Asia and Indonesia- where there are huge culture differences (for example, Nepal vs Gujarat) and huge language differences (Tamil Nadu vs Uttar Pradesh). So here is an example of a pluralistic, non centralized religion that is hugely popular among very many people.

Why is this? How can this be? Loot no further than the lack of centralization and the encouragement of tolerance in Hinduism. So if you want a common religion, have virtually no centralization, core tenants, except one of tolerance for the difference between people, and respect for the world around us.

Instead of looking to the extremely fractured religion of Christianity, as it implied by your use of the word "church", look instead to Hinduism.

In our world, in Hinduism, there is almost no centralization, and a huge variation in dogma and in what is considered scripture. There is even more variation in how scripture is interpreted, and a millions times more variation in ritual and religious practices. And this is in South Asia and Indonesia- where there are huge culture differences (for example, Nepal vs Gujarat) and huge language differences (Tamil Nadu vs Uttar Pradesh). So here is an example of a pluralistic, non centralized religion that is hugely popular among very many people.

Why is this? How can this be? Loot no further than the lack of centralization and the encouragement of tolerance in Hinduism. So if you want a common religion, have virtually no centralization, core tenants, except one of tolerance for the difference between people, and respect for the world around us.