Participation in the Mysteries required several months of preparation and respect for rules and restrictions so that the individual could accept and understand the revelation of secrets. The mystagogos was responsible for guiding the mystai. The content of the guidance is not entirely explicit. The mystagogoi probably undertook to prepare the faithful for the complicated or frightening elements of the worship that they would experience during the Mysteries. Perhaps they explained, to some extent, the content and form of what would happen, what would be said and what would be shown. The mystagogoi also supervised the fast that the mystai observed to purify body and soul in remembrance of Demeter's abstention from food during her search for her daughter.

The mystagogos supported the mystai throughout the preparation phase for the big night at the Telesterion. The mystagogoi accompanied the faithful to the sea for their cleansing, and the Great procession formed to return the sacred objects from Athens to Eleusis. On the night of the revelation, the mystagogoi led the mystai to the Telesterion.

Bay of Eleusis. Salamis across the bay, ca. 1875, photograph, Boston Public Library © Boston Public Library

It was the responsibility of the initiate to find a mystagogos. It is not clear whether the mystagogoi belonged to the gene of the Eumolpidae and the Kerykes. Still, the relevant market certainly included various fraudsters who lacked the necessary qualifications to act as mystagogoi but were very willing to receive the remuneration owed by the mystai to their initiators. However, the members of the Eumolpidae and the Kerykes had the right to advise the faithful, although it remains doubtful whether there were enough adult men in these gene to meet the demands of two or three thousand candidates each year in a one-to-one ratio. Creating groups of initiates with a balance of 1:10 could meet the market demand with two hundred mystagogoi, which would correspond to most available members of both gene. Possibly the pressure could be reduced by resorting to friends and acquaintances who had been initiated in the past, as is the case of Andocides, who acted as mystagogos for several of his guests or the orator Lysias, who promised to initiate his mistress Metaneira.