Initiation into the Mystery Religions
The ancient Mystery Religions had an initiation ceremony for those chosen to be come part of the private part of the religion.
There were typically three steps that could be taken in the private part of the Mystery Religions. Freemasonry also has three steps, or Degrees, even though it is not a religion.
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The steps:
1) Initiation into the Lesser Mysteries after purification by lustration. (??)
2) Greater Mysteries (??)
3) Perfection