The festival of Diwali falls on the last day of the Vikram calendar (Aso Amaas).The word "Diwali" is derived from the Sanskrit word "Deepavali" - Deepa meaning light and Avali, meaning a row.
In the west Diwali is referred to as the festival of lights as homes are lit with divas and no corner of the house is left in darkness. This is a tribute to the residents of Ayodhya celebrating the return of Shree Ramchandra Bhagwan and Shree Sitaji from their fourteen years of exile by lighting up the city in a similar way.
As already stated Diwali falls on the last day of the year. Earnings made in the year are respected through Chopda Poojan (worshipping of the account books). The New Year is welcomed and Shree Lakshmiji is invited into the house with the light from divas and colourful rangolii patterns. People look forward to the New Year bringing new wealth and the invitation of Lakshmiji (goddess of wealth) is vital for this.
However, Diwali is more a celebration of the triumph of good over evil than merely a festival of lights. The return of Shree Ramchandra Bhagwan to Ayodhya marks the slaying of the Ravana, the evil king of Lanka, who had kidnapped Sitaji and the safe return of Queen Sitaji to Ayodhya.
Furthermore, according to the Mahabharat, Shree Krishna Bhagwan killed the demon Narakaasur on this day. Narakaasur had kidnapped sixteen thousand devis and stolen the earrings of Aditi Mata (the mother of all the devtas). The devtas prayed for help and Shree Krishna answered their call by slaying this demon.
During His time on earth, Shriji Maharaj celebrated Diwali with great grandeur and festivity. He preached that these festivals are essential to remembering Bhagwan and His divine leelas. The festival of Diwali reminds us of how good always triumphs over evil and everyone should remember this when faced with adversity from evil forces.