What is Diwali (தீபாவளி)?

Diwali celebration is merited towards slaying if Hiranyakashya, return of rama from 14 years of vanavash, return of pandavas from 13 years of exile, But, the most common story we've all heard on the origin of diwali is slaying of Narakasura by Lord Sri Krishna. To be on same page, here is the most common version, please do pay close attention to the details like the description of characters and the numbers. These hidden in plain-sight clues will be interpreted later which everyone can leverage in betterment of day to day living and the yogis can immensely benefit in their spiritual journey.

1.) Narakasura is a son of Bhumadevi (Mother Earth) and Varaha (boar) Avatar of vishnu. 
2.) He is an asura (demon) king and ruled the Kamarupa kingdom and its capital city was pragjyotisha, surrounded by mystical mountains, utterly inaccessible and impregnable by others.
3.) It is also gaurded by 5-headed asura named Mura, 7 sons of narakasura.
4.) He invaded Bhur Bhuva Svaha, the 3 worlds. These 3 worlds are the earth, underworld a.k.a pishacha-loka (world of spirits) and the heaven a.k.a deva-loka (world of devas, demi-gods).
5.) Attacked Indra (king of devas) and captured the 4-tusked white elephant, gifted to Indra by Bhumadevi.
6.) Imprisoned Varuna and stole the crescent shaped ear ring of Aditi, Mother of all devas.
7.) Captivated 16,000 damsels and imprisoned them at Audaka on the top of the mountain Maniparvata in his kingdom. Narakasura's 10 sons gaurded the damsels.

Indra comes to Krishna and pleads to end Narakasura's tyranny. Since, Narakasura was cursed by Bramha that he'll die in the hands of a woman, Krishna ventures to the capital city of Pragjyotisha on his eagle-man, Garuda along with one of his wives Satyabama. Krishna fights and slays Mura (5-headed demon) the 7 sons gaurding the city and leads Satyabama for the final face-off and slaying of Narakasura. Releases the 16000 damsels, returns the Aditi's earring back and restores order, in the universe.

This story has several intrinsic details about how the rituals practiced during diwali impacts each and every individual. To start with, the author of these stories is Veda Vyasa, the same person who wrote the Bagawat Gita (and Mahabharatha). He is a Siddha, a fully attained yogi and adept in the attama-siddhi's bestowed only upon the very worthy of the meditators. Such a person, is not going to weave a story merely for entertainment. With his Aṇimā siddhi, he can observe the nuances of whats happening inside his body and narrates it as a story so the concepts gets imprinted in everyone who gets to hear it and when some of those individuals reach higher levels of consciousness, the same thought to be fictional stories, serve as a map or milestone to gauge their progress. As a matter of fact, Ramayana, Mahabharatha, Bagawat Gita, Srimad Bhagavatam, Soundarya Lahari, Skanda Shasti Kavasam, Vinayagar Agaval, Patanjali Stotras, Thirumandhiram, Thirukural, Thirupugazl and several such texts penned down by the siddhas is trying to convey the exact same thing at its core, but from different angles to cater to the varied approach and understanding.

Coming back to the story in hand, The devas and Asuras in any of these mythological stories are the personifications of the good and evil characteristics in every living being.

1.) Narakasura, son of earth and a boar, is the evil traits born of our desires for earthly pleasures and innate animal instincts.
2.) He ruled the kamarupa kingdom, which denotes the self-image and personality evolved out of our desires. This place being surrounded by mystical mountains are the layers of justification we assess to preserve this self-image.
3.) The 5-headed demon, Mura is the 5-senses; Sravana (hearing), Chakshusha (seeing), Jiva (taste), Nasika (sense of smell) and sparsha (touch). These 5 sense are turned outwardly protecting and nourishing these worldly desires.
4.) Invaded the 3 worlds, i.e., the material existence, good and evil nature. We start compromising these 3 aspects defining our personality towards attainment of these kamarupa desires.
5.) Indra's 4-tusked white elephant is the muladhara chakra with 4 petals. Muladhara represents our survival and this is the earthed chakra on which all other chakras function. Indra, Ganesha, Bramha and Darini are the four deities of Muladhara. The elephant symbolism can also be seen in representation of lord Ganesha. the functioning of this chakra and related endocrine glands, mainly the adrenaline glands, are hijacked towards these desires.
6.) The silver crescent shaped earring of Mother Aditi represents the nectar of vishuddhi chakra, the purification center of the 72,000 nadi network. When this is blocked, our ability to discriminate between right and wrong is severely paralyzed.
7.) Captivated 16000 damsels, these are the 16,000 Nadis that carry the pranic current towards spiritual evolution, in simple terms, that drives us towards actual manifestation of every individual. So, out of 72,000 nadis, 16,000 are blocked and we end up functioning only with the remaining 56,000 nadis, that are responsible for our day to day activities. When scientists says we are using only 5-10% of our brain, it is closely related to these dormant vital 16,000 nadis. Imprisoned in Maniparvata kingdom gaurded by 10 gaurds denotes the Manipura chakra with 10 petals, denoting the 10 pranas (Prāṇa, Apāna, Uḍāna, Samāna, Vyāna, Naaga, Koorma, Kirukara, Devadhatha, Dhanajaya).

Krishna, the yogi, traveling on garuda, the prana, with his 2nd wife Satyabama, the Ida nadi (breath from left nostril) enters muladhara, defeats 5-headed demon Mura, i.e., with strong determination, recoils from the pull of 5-senses. This phenomenon is also knows as pratyahara in ashta-anga yoga and also hails over 7 sons, retakes the control of sapta dhātu and leads satyabama, directs the cool prana via ida nadi into muladhara chakra and defeats Narakasura, stimulates the dormant kundalini shakthi to rise upwards. This Kundalini energy is the one that activates the ever dormant (since birth) 16,000 nadis. Along with these 16,000 nadis, there are 108 primary nadis, which are life vital and are explained in  detail in varma, and acupuncture. These nadis are collective called as 16108 wives of krishna. There is one other krishna has always been fond of, but not his wife, Radha, Sushumana Nadi. Restore the functioning of vishuddi chakra, the nadi purification center, with recovering the silver crescent moon shaped ear-ring of mother of devas, Aditi.

These details might sound very normal to someone in yogic path and well versed in the related books and artifacts, but strike as absolute bizarre and meaningless to someone who is hearing these words like nadis, chakras for the first time. Irrespective of it, take it with an open-mind and by chance if meditation descends on you, this will serve as a blueprint of what is happening and where it is leading you.

There is also an astrological significance as these days being the time of full debilitation of the sun in the whole year, meaning sun is exerting its least power and no moon day, meaning moon is at its least power at the same time. Hence a small window opens for a yogi, to get off the clutches of sun and moon's pull and evolve to higher realms. It doesn't mean one has to be a avid meditator to reap the benefits. Call it being in the right place at right time, anyone can leverage this window of opportunity to nitro-boost into a better state of anything deserved, be it level of creativity, wealth, social status, long pending goals, spiritual attainment, et al.

Coming to the rituals and meanings behind the fesitval, typically, Diwali is celebrated for 5 days.

Day 1 (in 2016, it is on 28th Oct)Dhanwantari Triodashi - Reevaluating perspective on Health

“shareeram aadyam khalu dharma saadhanam” (body is the best means for practising dharma)

This day is celebrated in adoration of Dhanwantari, Lord of Medicine for the devatas and originator of Ayurveda science. This is day for re-evaluating the perspective on health accumulated by any means. In the modern times, the sources are ample and the crisis is not the lack of information, but the right knowledge is piled over with too much unnecessary diversions. With the current level of our understanding and intelligence, this is the day to contemplate and discriminate between necessary and unnecessary advices on healthy living and take a vow to make necessary adjustments going forward.

Day 2 (29th Oct 2016): Naraka Chaturdashi - Detox physically and mentally

This is the day commonly celebrated as Diwali in southern regions of india.

“tena tyaktena bhunjeetaah” (this life can be enjoyed when detachment comes) – Isha Upanishad

The body has to be prepared for the energy burst that'll happen when 16,000 dormant nadis get activated. Hence on this day, people often get a rigid massage with the rightly prepared oil (Sesame seed oil, soaked with peppercorn and beetle leaves and warmed under sunlight) for 24 to 48 minutes and shower before sunrise. This is to activate the Ida Nadi. When the body is cooled down before the sunrise, the Ida Nadi become hyperactive, which facilities the flow of prana into Mooladhara chakra. Again, avid meditators should be able to experience this effortlessly. Any of the pranayama techniques like sudharsana kriya, shambavi mudra, naadi shodhana, kabalapathi, bastrika, sukha swasam, and so on will be more beneficial on this day.

Day 3 (30th Oct 2016): Aswayuja Amavasya - Renewal of Goals (Lakshya)

This is the day commonly celebrated as Diwali in northern regions of india.

This day is also known as Lakshmi Amavasya and is considered the jamadhin (birthday) of Lakshmi, goddess of wealth. The mind (moon) searches for the purpose of life (sun) and it tries to fix the goal (libra) due to the exact conjunction of sun/moon in libra that happens once a year on this day. This is commonly recommended for starting new business ventures.

Day 4 (31th Oct 2016): Govardhanpuja Pradhamai - Reassure the sense of being protected

"na me bhaktah pranashyati” (My devotees are never destroyed) - Bagawat Gita

Krishana lifted govadhan mountain to protect the people from the deluge of rain. When almighty (god/nature/conciousness/beyond/universe/unknown…call it whatever suits you) becomes the focus, all obstructions, sufferings, troubles come to an end. Meditating on realizing the effect of the surroundings on us and reassuring the sense of being protected by the universe is the theme of the day. Its a simple logic, we are here, as the universe intends to, if it doens't need us, we'll be wiped out in a blink of an eye.

Day 5 (1st Nov 2016): BhaiyaDooj Dwitiyai - Acknowledgement of sibling bond.
This is the time to rejoice the love, friendliness and harmony of co-existence. As per puranas, Yama, the Lord of Death has assured that he would not bother those mortals who spread the message of love to their brothers and sisters. A perfect harmony leads to moksha, the ultimate liberation. This 5th day is also the commencement of Shashti Viratham, another 6 days of fasting and rituals in honor of Lord Muruga (karithikeya, Skanda) which culminates as Soorasamharam (5th Nov 2016), we'll save this story for another day.

Thus this ‘Five-day Festival’ of Diwali traces the spiritual expansion of human growth culminating in the gaining of knowledge of beyond. It offers an opportunity to dive deep into one’s heart and search for all types of demonic qualities residing inside. Thus, the need is felt to clear the darkness from the heart. To dispel away the internal darkness we have to light the lamp of knowledge. When a lamp is lit on Diwali, just pray to your chosen ideal that the darkness of ignorance be removed from your heart.

With this understanding, reciting this Shanti Mantra (incantation of peace) at the start and end of the day, at the least on these 5 days, will bring a great sense of peace in everyone.

From Brihadaranyaka Upanishad (1.3.28);
asato mā sadgamaya
tamasomā jyotir gamaya
mrityormāamritam gamaya
Oṁ śhānti śhānti śhāntiḥ

From ignorance, lead me to truth;
From darkness, lead me to light;
From death, lead me to immortality
Om peace, peace, peace