Final answer:
Demeter taught Triptolemos the mystery of agriculture, specifically the cultivation of grain. He spread this knowledge across the land, contributing to human survival and civilization. The Eleusinian Mysteries celebrated these teachings, representing the life cycle, agricultural fertility, and possible allusions to an afterlife.
Step-by-step explanation:
The mystery that Demeter taught Triptolemos, according to the Homeric Hymn to Demeter and Eleusinian tradition, is associated with agricultural fertility and the cultivation of grain. Triptolemos was given the knowledge of agriculture by Demeter, who promised fields yellow with corn as a blessing. With this knowledge, Triptolemos was to spread the gift of agriculture to humanity, thus ensuring the fertility of the earth and sustenance for human civilization. The Eleusinian Mysteries celebrated these divine gifts and the sacred teachings, and while they were shrouded in secrecy, they primarily symbolized the life cycle of nature and the human hopes for a bountiful harvest and perhaps even an afterlife characterized by less tangible rewards.
These mysteries also reflect the cultural and religious importance of Eleusis in ancient Greek society. Triptolemos' role extended beyond his initial contribution to agriculture as he was later seen as a judge in the underworld in 4th-century traditions. The performance of the Eleusinian Mysteries focused on 'showing' rather than 'teaching', with an emphasis on the visual experience of the initiates, although the 'catechism' or preliminary initiation may have provided explanations of the rituals and their deeper significance, including allusions to eschatological hopes.