The Otherworldly must behave as his level 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 control over it yet.
The path roles are craft-based: the Apothecary prepares potions and understands compositions, the Beast Tamer lives among animals, the Potions Professor turns the craft into science.
The method long remained the knowledge of a few: church hierarchies were in no hurry to reveal it, and many otherworldly beings rose blindly, paying for it with their sanity.