Shakti is the spiritual energy of the Great Goddess that exists within each living being. Within the body, Kali is Kundalini, the "Serpent Power," the key to spiritual liberation.
Joseph Campbell (1904-1987), mythologist, author and television raconteur advised spiritual seekers to "follow your bliss." For Tantra initiates, "bliss" generally means the Great Goddess in her mystical and magical aspect, idealized and embodied as woman.
Kali is the Ultimate Shakti, the "Dark Secret of the Universe" and a potent initiatory power. To people unfamiliar with the inner meaning of wrathful metaphysical symbolism, Kali's many dark and fearsome forms might seem threatening. In Tantric tradition occult power is concealed behind scary symbols, to keep it accessible only to initiates.
Tantras teach that the physical universe is but an expression of certain primordial sounds or vibrations, the consonants and vowels of the Sanskrit alphabet, combined together in different ways. "Seed-syllables" (bija mantras) - short combinations, and "spells" (dharanis) - long combinations of differing measures, are the very "fabric" from which this universe is formed. The mystery of Kali's name, which begins with the first consonant of the Sanskrit alphabet, attached to the first vowel, is deep indeed. The use of mantras, repeated power phrases and spells, using language whose exact meaning is now largely forgotten or kept secret, is a common feature of archaic cultures where "magical arts" thrived.
"Kali Ma," the compassionate Primordial Mother, can be timeless and formless, young and old, exquisitely beautiful and alluring, as well as awesomely ugly and repugnant. She manifests as virgin and whore, young girl and sensual mature woman, a wrathful warrior queen and an old hag, nurturing mother and "wicked witch." Kali is a paradox to those who do not know her well. She seems unpredictable, yet to her devotees she is always reliable.
For practices of Tantra magic, meaning "Tantra-Mantra," Kali is the ultimate ally. Her seed-mantras "Kang" and "Kling" are all-powerful and are used in many different Tantric rites.