The incarnation of God as half masculine and half feminine is traditionally called Ardhanarishwara and represents the balance of forces that make up existence. Shiva is the embodiment of unmanifested conciousness that brings everything into existence and takes everything away. Shakti is the manifestation and actual form of that consciousness. She is the sacred energy that is life itself. As fire and heat are inseparable, so are Shiva and Shakti one. He is spirit and she is matter. He is the moon and she is the sun.