Why Divaalee is celebrated every year? There are many reasons to celebrate it....

(1) Goddess Lakshmee’s Birthday :
On this very Divaalee day, the Goddess of wealth, Lakshmee Jee is said to have been incarnated from the depth of the bottomless ocean. The Hindu scriptures tell us that both Devtaa (gods) and Asur (demons) were mortal (Mrit) at one point of time. Seeking a deathless condition (Amarattwa), they churned the ocean to seek Amrit, the nectar of immortality (an event mentioned in the Hindu scriptures as "Samudra Manthan"), during which a host of divine celestial objects came up. Prime among these was Goddess Lakshmee, the daughter of Samudra, who arose on the New Moon day (Amaavasyaa) of the Kaarttik month. She was subsequently married to Lord Vishnu on the same darkest night of the year and brilliant lamps were illuminated and placed in rows to mark this holy occasion. Hence the association of Divaalee with Goddess Lakshmee and the tradition of lighting of lamps and candles during the festival. To this day, Hindu celebrate the birth of the goddess Lakshmee and her marriage to Lord Vishnu on this day and seek her blessings for the coming year.

(2) The Legend of King Mahaa Bali :
The Bhaagavat Puraan, says how on a Divaalee day Lord Vishnu, in his fifth incarnation as Vaaman Avataar, rescued Lakshmee from the prison of King Bali during the Tretaa Yug. Bali, or rather King Mahaabali, was a powerful demon king who ruled the earth. Powered by a boon granted to him by Lord Brahmaa, Bali was invincible and even gods failed to defeat him in battles. Although a wise and perfect king otherwise, Mahaabali was violent in his ways with the Devtaa. So on their insistence, Lord Vishnu disguised himself as a short Braahman and approached Bali for some charity. The righteous and benevolent King couldn't refuse the Braahman's wish and was tricked into giving up his kingship and wealth (of which Lakshmee is said to be the Goddess). Divaalee marks this overcoming of Mahaabali by Lord Vishnu and this is another reason why Goddess Lakshmee is worshipped on Divaalee. In Kerala, the festival of Onam is celebrated around the month of August to mark this legend.

(3) The Killing of Narakaasur :
The Bhaagavat Puraan tells us about Naraakasur, an evil demon king who had managed to acquire awesome powers. Unrivalled in prowess, he conquered both, the Heavens and the Earth, and was tyrannical in his reign. Addicted to power, he even stole the earrings of Aditi, the heavenly mother goddess, and usurped some of her territory. When Lord Vishnu was incarnated as Krishn in the Dwaapar Yug, He killed Narakaasur on the day preceding Divaalee and rescued 16,000 women whom the demon had imprisoned in his palace. The deliverance from the terrible Narakaasur was celebrated with much grandeur, a tradition that continues to this day.

However, another version of the story credits Lord Krishn's wife Sathabhaamaa as the one who eliminated Narakaasur. It is said that Narakaasur could only be killed by his mother Bhoo Devee and as Satyabhaamaa was an incarnation of the same Bhoo Devee, only she could kill him. Before death, however, Narakaasur realized his mistake and requested a boon from Satyabhaamaa that everyone should celebrate his death with colorful lights. To commemorate his death, the event is celebrated in some parts of India as Naraka Chaturdashee, just before Divaalee day.

(4) The Return of the Paandav :
The great Hindu epic Mahaabhaarat reveals that it was Kaarttik Amaavasyaa day when Paandav's 12 years of banishment got over as a result of their defeat in the hands of the Kaurav at the Dice game (gambling). The five Paandav brothers, their mother and their wife Draupadee were honest, kind, gentle and caring in their ways and were loved by all their subjects. To celebrate the joyous occasion of their return to Hastinaapur and to welcome back the Paandav, the common people illuminated their state by lighting bright earthen lamps everywhere. And the tradition is maintained to this day.

(5) The Victory of Raam Over Raavan:
The great Hindu epic Raamaayan describes how Lord Ram conquered Lankaa after vanquishing Raavan and after passing a period of of fourteen years in exile returned to his capital Ayodhyaa on a New Moon day of Kaarttik with wife Seetaa and brother Lakshman. To celebrate the homecoming of their beloved king, the people of Ayodhyaa burst crackers, lit up their houses with earthen lamps (Diyaa), and decorated the entire city in the grandest manner. Year after year this homecoming of Lord Raam is commemorated on Divaalee with lights, fireworks, bursting of crackers and merriment. The festival gets its name Deepawali, or Divaalee, from the rows (Avali) of lamps (Deep) that the people of Ayodhyaa lit to welcome their King.

(6) Story of Nachiketaa :
An interesting story about Divaalee day is from the Kathopanishad where a small boy named Nachiketaa believed that Yam Raaj, the god of Death, was as black as the dark night of Amaavasyaa, but when he met Yam Raaj in person he was puzzled seeing his calm countenance and dignified stature. Then Yam Raaj explained to Nachiketaa on this Divaalee day of Amaavasyaa that only by passing through the darkness of death, man sees the light of highest wisdom. It is only then his soul can escape from the bondage of his mortal frame to mingle with the Supreme Power. It was then that Nachiketaa realized the importance of worldly life and significance of death. All of Nachiketaa's doubts were set to rest and he whole-heartedly participated in Divaalee celebrations.

(7) Coronation of Vikramaaditya :
It is also said that Raajaa Vikraamaditya, the legendary Indian king famed for his wisdom, valor and magnanimity was coroneted on the Divaalee day following his victory over the Shak in 56 BC. This was marked by a grand celebration which is still maintained annually. One of the greatest Hindu monarchs, Vikramaaditya ruled the greatest empire in the world from modern-day Thailand in the East to the borders of modern-day Saudee Arabia in the West. Divaalee, thus, apart from being a religious festival also has a historical association.

(8) The Enlightenment of Swaamee Dayaanand Saraswatee :
Divaalee also marks the auspicious occasion when on a New Moon day of Kaarttik (Divaalee day) Dayaanand Saraswatee, one of the greatest reformers of Hinduism attained his Nirvaan (enlightenment) and became Maharshi Dayaanand, meaning the great sage Dayaanand. In 1875, Maharshi Dayaanand founded the Aarya Samaaj (literal meaning is Society of Nobles), a Hindu reform movement to purify Hinduism of the many evils it became associated with at that era. Every Divaalee, this great reformer is remembered by Hindusall over India.

(9) The Enlightenment of Vardhamaan Mahaaveer :
For Jain, Divaalee commemorates the enlightenment of Vardhamaan Mahaaveer (the 24th and the last Teerthankar of the Jain and the founder of modern Jainism) which is said to have occurred on October 15, 527 BC. This is one more reason to engage in Divaalee celebrations for pious Jain and other than the purpose of commemoration, the festival stands for the celebration of the emancipation of human spirit from earthly desires.

(10) Special Day for the Sikhs :
For Sikhs, Divaalee holds a special significance for it was on a Divaalee day that the third Sikh Guru Amar Daas institutionalized the festival of lights as an occasion when all Sikhs would gather to receive the Guru's blessings. It was also on a Divaalee day in 1619 that their sixth religious leader, Guru Hargobind Jee, who was held by the Mugal Emperor Jahaangeer in the Gwalior fort, was freed from imprisonment along with 52 Hindu Kings (political prisoners) whom he had arranged to be released as well. And it was also on the same auspicious occasion of Divaalee when the foundation stone of the Golden Temple at Amritsar was laid in 1577.

(11) Goddess Kaale :
Kali, also called Shyaamaa Kaalee, is the first of the 10 Avatars (incarnations) of Goddess Durgaa, Lord Shiv's consort. According to legend, long ago after the gods lost in a battle with the demons, Goddess Kaalee was born as Kal Bhoi Naashinee from the forehead of Goddess Durgaa. Said to be a personification of Naaree Shakti (female power), Kaalee was born to save Heaven and earth from the growing cruelty of the demons. After killing all the devils, Kaalee lost her control and started killing anyone who came her way which stopped only when Lord Shiv intervened. The well-known picture of Maa Kaalee, with her tongue hanging out, actually depicts the moment when she steps on the Lord and repents. That momentous day has been commemorated ever since and the main purpose of celebrating Kaalee Poojaa is to seek the help of the goddess in destroying evil both external and internal to us as also to get her blessings for general happiness, health, wealth, and peace.

To conclude, there are several reasons behind Divaalee celebrations and almost every region of India has its own reason to observe the occasion. All of these however, matters little to the festival itself. Whatever the cause behind its celebration, Divaalee is undoubtedly a national festival of India, and the aesthetic aspect of the festival is enjoyed by most Indians regardless of faith.