Note: The use of "when" in the question presupposed that the "one God" part is true. I don't actually remember whether the original question was posed using "when" or "if".
mm: There is only one reality, but many, many descriptions of this reality.
Q: "Reality" is like a vicious dragon to me, I don't understand what you are talking about.
mm: If God is a part (or whole) of the reality in which we live, undoubtedly, people would describe God in many defferent ways, different groups of people then hold on to these different descriptions to form their religions. But if God isn't a part of the reality in which we live, well then, the many religions are just like different TV networks that want more veiwers.
What's God anyway? And why "one"? "One" is only a conceptual article (term) that is quite usuful when we communicate with one another that has a common meaning (e.g., one apple). But what does it mean when used in front of the word "God"? "God" isn't a "thing", right? So what's the fuss about whether there's only "one" God or "two" or "many" gods?
Folks, I am not a linguist, so all these terms... I don't understand, This is just a part-time gig I take on "five days a week", I ain't no rocket man.