Oracles exist so that priests can control whole populations. The Greek oracle was the tool of the priesthood, who conveniently served as interpreters of her words to kings.
The priests of the Christian Church once kept Bibles chained to pulpits. This made them the only ones with access and thus the ability to interpret scriptures.
There is obviously something very powerful in pursuing divine or sacred knowledge as an individual. It is this power that elites have always feared.