The otherworldly must behave as their level dictates until the power becomes part of them. Until the potion is digested, the carrier is vulnerable: the power is already there, but control over it is not yet.
The roles of the path involve risk and stakes: the carrier repeatedly puts the outcome on the line and learns to live with what they are dealt.
The method long remained the knowledge of the few: the hierarchs of the churches were in no hurry to reveal it, and many otherworldly beings rose blindly, paying for it with their sanity.