The ancient Greek religion had a strong public character. Each city worshipped its gods in public view and with pandemic participation, while the majestic religious ceremonies and sacrifices functioned as a method of integration of individuals in society and in the body of citizens.

Along with the public religion of the city-state, however, there were special cults to which each believer came on a voluntary basis as an individual. The ancient Greeks called these religious events "Mysteries". The Mysteries were radically different from the official cult that sought the favour of the gods for the benefit of the city and the citizens as a whole. Participation was not limited by the gender or social status of the candidate secretaries. It was not obligatory or inevitable, but it was an expression of personal will and free will.

The main function of the Mysteries was to help mortals who faced the fear of death. They were addressed to the inner world of the believers and were characterised by a great degree of secrecy. Believers became acquainted with the content of the Mysteries by participating in an initiation ceremony, which formed a new, better relationship between the individual and the uncle. After the end of the ceremony, the participants could claim to have a higher degree of truth (compared to the ignorant), having experienced a piece of the essential and eternally unchanging reality. Although their appearance remained unchanged, the mystai had experienced a shocking experience that transformed the way they thought and perceived things.

A special feature of the Mysteries was the avoidance of revealing their contents to those who had not participated in the initiation ceremony. The ancient Greeks distinguished between "secret" (what cannot be said in words) and "secret" (what is forbidden to say in words). The Mysteries revealed to the faithful supreme truths about which the mystai could not and should not speak. The ban could be imposed either by legal restrictions introduced by the state or because of the piety of the faithful and the fear of divine wrath and punishment in case of violation of the principle of secrecy. The result is the absence of extensive or specific information about the essence and form of most ancient Greek sacramental ceremonies.

The Mysteries are not exclusively a Greek phenomenon but played a decisive role in the religious and social life of the ancient Greeks. Their birth dates back to the Mycenaean years, although there is no doubt that their distant roots are lost in even older times. Some Mysteries were performed (in small variations) in many parts of the Greek world, while others were characterised by a strong connection with specific locations. The Mysteries of Dionysus and Orpheus were held in private gatherings, away from the "spotlight". There is no specific centre of Bacchic worship. The worship of Demeter and Persephone, on the other hand, seems almost unthinkable far from Eleusis, where according to legend the reunion of the gods took place and the knowledge of the cultivation of cereals was transferred from the gods to humans. The Eleusinian cult is distinguished by the evocative connection of the personal contact of gods and mystai in the context of a multi-day public religious ceremony, which included mass purifications, dances, sacrifices and the imposing procession from Athens to Eleusis.