RCA, you've missed my point. You are assuming that beliefs can be neutral, and that is not philosophically cogent. There are several problems with your response, first of all. When you said that "Religious belief requires being tied to a formal religion and being subjected to its rules and doctrines," I need to know what you mean by "formal religion," because I'm pretty sure that your definition of "formal religion" will be different from mine.
Beliefs are inherently religious, RCA, because beliefs are based on faith in someone or about something. More importantly, beliefs reveal the nature of your worldview, insofar as telling us what you found your knowledge, reality, and ethics upon to understand the universe. If you believe that 2+2=4, that reveals a number of faith-commitments you have about the existence of immaterial concepts (like numbers and arithmetic), the laws of logic, the uniformity of nature, the idea that memory is reliable, the belief that mathematics is objective, the belief that numerical values maintain their identity throughout time and space, and a host of other faith-commitments that are assumed without the aid of natural science. Beliefs are not held in isolation; they are connected to other beliefs, depending on one's worldview. That is why a belief can never be neutral.
Going back to your original question, when you asked it, did you bother to consider what you meant by "God" or "afterlife"? You have to understand that those terms can mean different things to a multitude of people. Yet, your question, itself, assumes that there is a particular understanding of "God" and the "afterlife," which you have made up in your mind. You should have been more specific about the question by asking a better one, perhaps, "What religion makes it necessary that God and the afterlife should be discussed together?" That pins it down to a particular worldview analysis, and not just some "neutral," open-ended inquiry that treats all religions the same, especially when dealing with infinitely deep subjects like God and the afterlife.