I read a terrific description of shakti and shiva in Stephen Copes book Yoga and the Quest for True Self. I love dancing and the imagery in this excerpt made my spine tingle!
(Note: Shakti, when capitalized, refers to the goddess – Shivas consort – who is the embodiment of the feminine principle; in lower-case, shakti refers to the nonpersonalized principle of pure energy itself.)
You might think of Shiva (the masculine principle in creation) as the still point, the absolute subject, the One. And Shakti (the archetypal feminine) as the dance. Its like T.S. Eliot said – Without the still point, there would be no dance.
In the yogic view, the entire universe moves between these poles – shiva and shakti. Pure consciousness and pure power. Pure being and pure becoming. The still point and the dance. Always arcing toward one another.
In hatha yoga – the practice of postures and yogic breathing – the whole drama of the universe gets acted out within this very earthly body. In this drama, all the condensed powers of shakti lie coiled at the base of the spine. This is what we know as kundalini, the essence of divine goddess energy. The kundalini shakti longs to rise up to meet her consort, shiva, pure witness consciousness, who resides in an energy center at the crown of the head, the so-called crownchakra.
The union of shiva and shakti, which is the goal of hatha yoga, is accomplished when shakti moves up through the energy column in the area of the spine – called the shushumna – and arrives at the crown. On its trip to meet shiva, this highly condensed energy of kundalini shakti awakens all of the latent energy centers in the body, and as this happens, the body moves spontaneously into hundreds of postures. The dance that results is the interplay of energy and consciousness, or what yogis call lila – the divine play.
S. Cope, Yoga and the quest for the true self (New York: Bantam Books, 1999) p. 52-53