Deepawali or Diwali is certainly the biggest of all Hindu festivals. It's the festival of lights (deep = light and avali = a row i.e., a row of lights) that's marked by four days of celebration, which literally illumines the country with its brilliance and dazzles all with its joy. Each of the four days in the festival of Diwali is separated by a different tradition, but what remains true and constant is the celebration of life, its enjoyment and goodness. more details http://www.hindufestivals.org/festival_of_lights_diwali_deepavali.html
The Origin of DiwaliHistorically, the origin of Diwali can be traced back to ancient India, when it was probably an important harvest festival. However, there are various legends pointing to the origin of Diwali. Some believe it to be the celebration of the marriage of Lakshmi with Lord Vishnu. Whereas in Bengal the festival is dedicated to the worship of Mother Kali, the goddess of strength. Lord Ganesha, the elephant-headed God, the symbol of auspiciousness and wisdom, is also worshipped in most Hindu homes on this day. In Jainism, Deepawali has an added significance to the great event of Lord Mahavira attaining the eternal bliss of nirvana. Diwali also commemorates the return of Lord Rama along with Sita and Lakshman from his fourteen year long exile and vanquishing the demon-king Ravana. In joyous celebration of the return of their king, the people of Ayodhya, the Capital of Rama, illuminated the kingdom with earthen diyas (oil lamps) and burst crackers. more details http://www.hindufestivals.org/festival_of_lights_diwali_deepavali.html
These Four DaysEach day of Diwali has it's own tale, legend and myth to tell. The first day of the festival Naraka Chaturdasi marks the vanquishing of the demon Naraka by Lord Krishna and his wife Satyabhama. Amavasya, the second day of Deepawali, marks the worship of Lakshmi, the goddess of wealth in her most benevolent mood, fulfilling the wishes of her devotees. Amavasya also tells the story of Lord Vishnu, who in his dwarf incarnation vanquished the tyrant Bali, and banished him to hell. Bali was allowed to return to earth once a year, to light millions of lamps to dispel the darkness and ignorance, and spread the radiance of love and wisdom. It is on the third day of Deepawali — Kartika Shudda Padyami that Bali steps out of hell and rules the earth according to the boon given by Lord Vishnu. The fourth day is referred to as Yama Dvitiya (also called Bhai Dooj) and on this day sisters invite their brothers to their homes.
The Significance of Lights & FirecrackersAll the simple rituals of Diwali have a significance and a story to tell. The illumination of homes with lights and the skies with firecrackers is an expression of obeisance to the heavens for the attainment of health, wealth, knowledge, peace and prosperity. According to one belief, the sound of fire-crackers are an indication of the joy of the people living on earth, making the gods aware of their plentiful state. Still another possible reason has a more scientific basis: the fumes produced by the crackers kill a lot of insects and mosquitoes, found in plenty after the rains.
The Tradition of GamblingThe tradition of gambling on Deepawali also has a legend behind it. It is believed that on this day, Goddess Parvati played dice with her husband Lord Shiva, and she decreed that whosoever gambled on Diwali night would prosper throughout the ensuing year. From Darkness Unto Light...In each legend, myth and story of Deepawali lies the significance of the victory of good over evil; and it is with each Deepawali and the lights that illuminate our homes and hearts, that this simple truth finds new reason and hope. From darkness unto light — the light that empowers us to commit ourselves to good deeds, that which brings us closer to divinity. During Diwali, lights illuminate every corner of India and the scent of incense sticks hangs in the air, mingled with the sounds of fire-crackers, joy, togetherness and hope. Outside India, Diwali is more than a Hindu festival, it's a celebration of South-Asian identities. If you are away from the sights and sounds of Diwali, light a diya, sit quietly, shut your eyes, withdraw the senses, concentrate on this supreme light and illuminate the soul.