It wasn’t until the late Roman Empire that what you believed in your mind really became important in religion. Before that, performing the rituals correctly was far more important.
Do you have any good resources in mind on this topic? I've been reading Boyarin's Border Lines, which hypothesizes that the concept of religion was created around that time to describe what kind of thing Christianity was, and to explicitly separate it from Judaism (which was cast as another thing of the same type by both sets of leaders). Really interesting perspective.
