The origin of the phenomenon described above lies in actual worship of the female sex organ. A young, healthy and beautiful woman, properly bejewelled, profusely perfumed, and consecrated through meditation and yoga, became herself an object of worship, with her yoni (vulva) symbolizing the Cosmic Womb. A state of infinite bliss was achieved through a gradually intensified love, focused at first on a human lover in physical love, and then transferred to the transcendental state, of which human love is just a reflection.
Any symbol is merely a symbol for something else, and that “something else” is the Innermost Reality. A symbol or an image is created to be used as one of the means in the process of experiencing that Reality. Through invocation and meditation, life is infused into the symbol. The yogi in his sadhana goes beyond sound (mantra) and sight (yantra) and dissolves himself as well as the symbol to embrace and become bliss. The symbol is thus left behind and becomes a museum piece. The invocator and the invoked merge into one consciousness, leaving behind a relic.
These relics are found in ancient cultures other than the Hindu and Buddhist, where the female principle was represented as a goddess. To make the female god morally acceptable, she was called mother goddess or Mother Earth.