Enneads VI.9: Of the Good and the One
Illustration from the Secrecy of the Mystery-rites
11. That, no doubt, is the meaning of the mystery-rites’ injunction not to reveal their secrets to the uninitiated. As that which is divine is unspeakable, it is ordered that the initiate should not talk thereof to any (uninitiated person) who have not had the happiness of beholding it (the vision).