The Otherworldly must behave as his stage prescribes, until the power becomes part of him. Until the potion is digested, the bearer is vulnerable: the power is already there, but there is no authority over it yet.
The learned roles: The Priest of Secrets keeps and passes on the hidden, the Mysticologist dissects rituals piece by piece, the Sage answers those who came for wisdom.
The method long remained the knowledge of a few: the church hierarchs were in no hurry to reveal it, and many Otherworldly ascended blindly, paying for it with their sanity.