Jung spent considerable time examining and explicating the role of the Mother archetype in the psychology of the unconscious, and there is a large, rich literature on this archetypal dominant both in his "collected works" and in the works of his followers. Her, Jung delineates some characteristic aspects of the Mother archetype as it often appears in mythology and religion....
"The Mother Archetype" - Carl Jung
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Why is the archetype of the great mother often dark and frightening at first encounter? Is it only because she was made unknown by church cultures? Or must she be unknown by definition because she is the opposite of intellect ? James Bennett, in his book “Underworld & Archetypes Fully Illustrated” declares she is matter, substance itself.; and casts a new light on the neglected gods of the Mythological Underworld: Hela, Cybele, Isis, Kali, Hecate, Cerridwen. See http://tiny.cc/nrvrux