The image of Goddess Kali is full of hidden symbolism.
- Her dark colour represents the infinite.
- The name Kali refers to her colour, which is black, and represents the infinite. But it also refers to time. That itself gives us a clue to her function, because time, space, and causation are all processes of maya, the great illusion. Time, as we all know, truly is the all-destroyer. Nothing in this world can escape from destruction due to time.
- Her three eyes represent knowledge of the past, present, and future.
- Kali has four arms, representing the dualities of this world. Her two right arms represent the benign aspect. She bestows fearlessness and boons with those. While her two left arms, holding a sword and a severed head, and most of the rest of her, represent the terrible aspect. Here we have her function of causation — creating and destroying, as well as of the dual experience in this world. Everything comes from her and everything dissolves back into her.
- Her red tongue sticking out represents rajas, the quality of activity.
- Her white teeth, pressed on her tongue, represent sattva, the quality of calmness.
- Both then represent the quality of activity being controlled by calmness.
- The garland of fifty skulls represents the fifty letters of the Sanskrit alphabet, which also means speech.
- The sword in her upper left hand cuts our ignorance, or bondage.
- The severed head in the lower left hand is said to bestow wisdom.
- As Kali stands on Shiva, who represents the Absolute aspect of God, so Kali represents the cosmic power, or Shakti, that brings creation into being.
Source - Article titled Why Mother Kali? by Pravrajika Shuddhatmaprana Published in the Prabuddha Bharata January 2016 issue.