Ancient religion developed long before writing did, so our knowledge on this topic is incomplete. Religions arose naturally in all parts of the world, indicating that there is a religious instinct deep inside humans. Humans develop a religious life to try to make sense of transcendent things that they can't control or explain. They know they are not in control of the world, so they search for who or what is.
Anthropology teaches us that the religious process begins with experience. People reflected upon their experiences, and from there, they generated religious rituals and beliefs. Ritual can be seen as the primal act of religious instinct; you can even find them in cultures without a god. Rituals are designed to align people to the sacred reality; they are an interaction with the divine. Often, rituals are repetitive and imitate what they're supposed to produce.
One important element of ritual is sacrifice. Sacrifice literally means "to make something holy (sacro)". Sometimes this involves injecting holiness into something profane, but usually it is a recognition of something that is already holy. Sacrifice points to an awareness that reality is holy.
A second important element of ritual is the meal, which has always been tied to sacrifice. In a normal meal, the meal energizes us and connects us to the world we got the food from. In a sacred meal, there is an exchange; the meal gives nourishment to the human, and the human's labor creates the meal. From what we can tell, the sacred meal predates belief in gods. When beliefs in gods develop, the original beliefs connected to the sacred meal are changed.
We cannot point to a specific moment in history where the idea of God appeared. We know that, after the development of ritual in the ancient world, the development of myth followed. A myth is a narrative account of a sacred reality that serves to bring meaning and coherence to human existence. An example would be the Enuma Elish, the Babylonian creation story.
Myths come from the reflections upon the rituals. They tend to lead one back to the rituals; that is, they explain why certain rituals work. They give us greater understanding into the rituals, and people tend to bring this greater understanding into the rituals. This ends up being a circular process; the myths influence the rituals, which influence the myths, which influence the rituals, and so on.
Rational theology is myth in intelligible form. For example, our creation story in Genesis is a myth that explains how creation came about. The myth came out of a reflection of the Jewish experience of God. This is why Genesis has two creation myths; one focuses on the goodness of creation, while the other focuses on the dignity of humanity.
So that's how ancient religion developed. First there was experience, which gave rise to rituals and beliefs. These led to myths, which led to rational theology. All of these "stages of religion", we might call them, work together simultaneously and influence each other.
- The corruption of ritual is magic, where people start to think rituals are used to control the divine, whereas ritual is supposed to lead us to the divine.
- The corruption of myth is idolatry, when we think myths completely describe reality and refuse to change them. In this way, we close ourselves off to reality. Instead of opening us up to the divine, the myths put the divine in a box.
- The corruption of rational theology is rationalism, when rational theology confines itself to human thought. It doesn't return its insights to myth and ritual, but just stays where it is.