if there was only one religion?

Let's say that for the sake of argument that only one religion has existed throughout the course of history, there were never other religions or denominations of those religions.

With this belief is the standard idea of a heaven and hell, eternal reward and punishment. To gain this reward requires you to acknowledge that God is the creator and lord of all life as well as living a life as a good person.

Would the argument still hold any flaws in such a scenario?