It is said that on the day of Deepawali, a person who donates a lamp in the evening never fears the enemy and happiness and good fortune increase in his life. This lamp is performed on the banks of the river. The great importance of bathing in the Ganges on the day of Dev Deepawali has been told in the scriptures. It is believed that bathing in the Ganges on this day gives auspicious results throughout the year. Not only this, if duly done with a lamp, then the bad effects of Yama, Shani, Rahu and Ketu are reduced.
Lord Vishnu took Matsya avatar on this day
According to Hindu scriptures, on this day Lord Vishnu, the protector of the world, took the incarnation of Matsya (fish). Matsya avatar of Lord Vishnu is the first incarnation of his ten incarnations. In this incarnation, Lord Vishnu saved this world from a terrible flood. Along with this he also killed a demon named Hayagriva. It is said that Hayagriva stole the Vedas and hid them in the depths of the ocean.
Shiva had broken the ego of the demon king Tripurasura (Dev Deepawali story)
The holy festival of Dev Diwali is celebrated to commemorate the victory of Lord Shiva over the demon king Tripurasura. According to the legend, there was a demon named Tripurasura. He had stricken humans on earth and all the gods of heaven with his terror. The deities were also troubled by the wrath and terror of Tripurasura. After this all the gods reached Shiva and praying for help, prayed for the end of the demon king Tripurasura.
Accepting this request of the gods, Shiva killed the demon Tripurasura on the day of Kartik Purnima. At the end of Tripurasura Rakshay and his liberation from terror, all the deities lit a lamp in heaven with delight. After this, everyone came to Kashi, the city of Bholenath, took a bath in the Ganges and expressed their happiness by lighting a lamp in Kashi.
Since then every year on the full moon of Kartik month it is called Dev Diwali. On this day special lamps are lit at Kashi and Ganga Ghats, Dev Diwali is celebrated. On this day the demon king Tripurasura was killed, hence Kartik Purnima is also known as Tripuri Purnima and Tripurari Purnima.