Of course it is both. Religions are nothing but a system of beliefs (and practices), and beliefs or ideas in general have power over those brains they have "infected". People have sacrifices their lives, or killed other people because ideas told them so. They do have power!
And , secondly, ideas can have this power because people identify with a group that is hold together by certain ideas. This sense of belonging is like fuel added to the power of the ideas.

" The desire to belong in most people is greater than the desire to understand. Hence, the popularity of religion and cults and the lack of the role of reason in human affairs." Thomas Szasz

In many cases, both.