Why does Dune have such fundamental changes to major religions?

Question

In the Dune series, various religions have undergone drastic transformations. Judaism seems to be largely "intact," but both Christianity and Islam appear to have been substantially mixed with Buddhism. For example, Wikipedia's list of religion in Dune includes Mahayana Christianity, which it describes as

A hybrid of Mahayana Buddhism and Christianity, which presumably interpreted Jesus Christ as a Buddha.

Given that virtually all branches of Christianity regard Christ as God, this seems like a rather fundamental change. Islam doesn't seem to be all that amenable to hybridization with Buddhism either.

Why did so many of the religions of Dune appear to have been mixed with Buddhism at some point? And how does it account for such fundamental changes to the religions? Did this reflect a poor understanding of what doctrines of Christianity and Islam were important on Herbert's part?

Answer 1

Religions are no constants. They have always interacted with each other and with society and are rather flexible. Consider Mormonism, which started as a syncretism of Christianity and freemasonry. In less than two centuries, it changed major tenets like polygamy, racism, etc. because they were not practically compatible with society. Older religions are not immune to this either, just compare modern Protestantism with the Catholicism of the Middle Ages.

Now, Dune happens ten thousand years into the future. It is only to be expected that religions will fundamentally change and merge in such a long time. Which religions will take part in these processes with what outcome is impossible to predict; so Herbert’s guess is as good as any.