This is a term designating the underlying spirituality of Wicca reflected in the seasonal rites of Nature, along with the metaphors linked with the lunar reverence. The essence of this mythos is based upon the Wheel of the Year, which designates the sabbats of the Wiccan religion. The Wheel possesses the foundation of the Wiccan belief in ever-returning cycles, an aspect also linking the Wiccan belief to reincarnation. Death and the survival of the soul or spirit are important elements of the Mystery Teachings contained within the Old Religion.
Since Wicca is essentially an agrarian Mystery Tradition every aspect of plowing, planting, growing, and harvesting has symbolic meaning in the journey of the soul. These agricultural Mystery Teachings are involved with loss, return, death, and rebirth. The death and rebirth concepts are perhaps best depicted in the ancient myths of Demeter and Persephone that illustrate the foundation of the Wiccan concepts to the descent of the Goddess into the Underworld. This mythos is found in the early civilizations of Mesopotamia. The Agricultural Mysteries are also involved with transforming and changing the states of consciousness. (see Altered States of Consciousness) Such involvement stems from ancient times when psychotropic plants such as hallucinogenic mushrooms and fermented liquids were used. This branch of the Mystery Tradition is often referred to as the Fermentation Mysteries, and includes as well the Harvest Mysteries. The latter symbolically reveals the ancient mysteries through a variety of myths of slain and resurrected gods.
The Slain God or Divine King is an integral part of the Wiccan mythos and Mystery Tradition. He is closely connected with the life cycle of the plant kingdom and shares the characteristics related to planting and harvesting. The blood of the Slain God/Divine King possesses the same vital life-giving principle, as does the seed. Therefore, the mythos states that all must be returned to the soil so that life and abundance will fill the coming year.
The Wiccan mythos also includes the seasonal cycles of Nature known as the waxing and waning tides of the earth. These are the growth and decline forces that are often personified as mythical figures. In many Wiccan Traditions these figures are the Oak King and the Holly King. Other Traditions use an older, more primal set of figures, the stag and the wolf. Which ever is the case, the mythos is one of life and death. The one figure supersedes the other in an ever-repeating cycle. As it is seen with the Oak King and the Holly King, one figure slays the other during the solstice. The stag and wolf are slain by exterior factors representing the forces of Nature.
In the classic Wiccan Mythos there are various myths connected to each of the eight sabbats. At the Winter Solstice the new sun is born. At Imbolc the sun god reaches maturity and is purified as he prepares to encounter the Goddess. The Spring Equinox marks the return of the Goddess from the Underworld. At Beltane the God and Goddess meet to begin their courtship. The Summer Solstice marks their wedding and finds the Goddess pregnant from their union at Beltane. Lughnasadh marks the fullness of the Harvest, and the sun god becomes the Harvest King, the Slain God. The Autumn Equinox begins the descent of the Goddess into the Underworld in search of the Slain God of the Harvest. At Samhain they meet again in the Underworld, unrecognized at first. There they fall in love anew and exchange their mysteries. He gives to the Goddess the necklace of rebirth and she teaches him the mystery of the cauldron of rebirth. A.G.H.
Source: 78, 398-399.