According to the narrative from the Devi Mahatmya of the Markandeya Purana, the form of Durga was created as a warrior goddess to fight a demon. The demon's father Rambha, king of the demons, once fell in love with a water buffalo, and Mahishasur was born out of this union. He is therefore able to change between human and buffalo form at will (mahisha means "buffalo"). Through intense prayers to Brahma, Mahishasura had the boon that he could not be defeated by any man or God. He unleashed a reign of terror on earth, heaven and the nether worlds.
Eventually, since only a woman could kill him, the trinity bestowed a dazzling beam of energy upon the Goddess Trinity (Saraswati, Lakshmi, and Parvati), transforming her into the Goddess, Durga. Her form was blindingly beautiful with three lotus-like eyes, eight powerful hands, lush black hair with beautiful curls, a red-golden glow from her skin and a quarter moon on her forehead.


Each god also gave her their own most powerful weapons, Rudra's trident, Vishnu's discus, Indra's thunderbolt, Brahma's kamandal, Kuber's gada, etc. Himalayas gifted her a fierce whitish golden lion. On the end of the 8th and beginning of the 9th day of waxing moon, Chanda and Munda came to fight the goddess. She turned blue with anger and goddess Chamunda leaped out of her third eye. Her form was the most powerful one with 3 red eyes, blood-filled tongue and dark skin; who finally killed the twin demons with her sword. This form of the divine goddess is worshipped during the sandhikshan of Durga Puja festival, as sandhi/chandi puja. Finally on the tenth day of waxing moon, goddess Durga killed Mahishasura with her trident. In the mythologies, the Goddess does kill the demons and ends the existance of evil on the earth to ensure the man kind lives well on the planet.

But through the ages, the devil has again been dwelling as manifestations of the ignoble passions in human mind. like the very evils of dowry killing, female feoticide, bribery, red tapism, castism.
Those were the ages when the Humane race was endangered for the fear of the devils who would kill them for power. Even today, the devils in the minds of Human still starving for power, make them toil again their own race.
Celebrating the festive season from Navratri to Dussehra to Dipawali as the symbol of triumph of good over evil is no use unless we kill the demons residing inside ourselves who dont hesitate to kill our own fellow beings for greed.

The sole reason behind the creation of Godess Durga becomes void if we fail to live with love and affection as we were intentend to be, in a world lacking the devil. And demons inhibiting in our minds have to be thrown out to complete the omen of these pious festivals.