It is difficult to define the word “religion.”
We often speak of “a religion,” but within that religion, there are many sub-groups with different beliefs and rituals. These sub-groups tend to be localized in time and space.
New religions usually branch off of older religions.
Religions evolve over time.
I often conceptualize a religion in terms of its beliefs, but this likely wasn’t always the case. Religion has often been a group with set rituals and customs.
But is the distinction between belief and ritual real? Perhaps they are different views into the same reality.
A human’s actions can be determined by it’s internal state (its memory of the past and its beliefs and implicit ethical system) and external stimuli.
Rituals are one sort of human action, but all human actions (even outside of formalized ritual, but the little decisions of daily life) are determined by beliefs and memories, implicitly or explicitly. If one defines a belief very broadly, such that it does not need to be explicitly considered by the holder, then even primitive humans performing rituals must have implicitly believed they should have performed the ritual. When generalized in this way, belief and ritual may be one and the same.
I care more about beliefs because one can ask “are they true?” I care about truth because it will affect how I live my life. Thus, I care about ritual because it lets one deduce the implicit beliefs of a people, and by studying the evolution of beliefs in various religions and judging whether we think these systems are true, we can find epistemological principles which can guide us when we evaluate whether other religions are true.