Durga is a symbol of energy. Since the universe is born through energy, it is called Mother. All are born through a mother, therefore, the power which has given birth to the universe is known as Mother, Shakti, Energy or Durga.
The eight arms of Durga are representative of eight principles of energy. The world is grasped by five senses which are eyes, ears, nose, tongue and skin. Without these senses we cannot be in touch with the world. If we drop a curtain on these five senses, we will not feel the world, we will not be in the world, we will be cut off. These five senses are related to three great principles which are known as time, mind and space. Five senses plus these three principles make a total unit and these eight principles are known as the eight arms of the divine power. Without these we would not be able to relate ourselves to the world.