Lord Vishnu incarnated Kurma Avatar in Sat- Yug to help devtas from Asuras. Though Devtas and Asuras were cousins, they were at war all the time. Day by day the tension between Devtas and Asuras grew and as a result of that gods were losing their strength due to the extreme curse* that was given to them by Saint Durvasa. As a result of that devtas were on the verge of defeat as they were helpless and their forces were dead in large numbers. They approached Lord Brahma and pleaded for help. Brahmaji meditated for a while and then said, “Let’s take refugee in Lord Vishnu. He always helps those who have faith in him.”
Lord Vishnu advised them, “To defeat Asuras, you will have to strive hard and obtain Amrit (the nectar of immortality) by churning the ocean and that’s the only way out for you.”
Hearing this Indra asked lord Vishnu that how could they churn a Ocean? Vishnu replied,”Churn the ocean of milk after adding medicines (all kinds of plants, grasses, herbs & creepers) into the ocean to get the Nectar of immortality. Use Mount Mandarachal as a churning stick & Vasuki (king of serpents) as a rope to turn the mountain”. But one more question arose that how can devtas move mount Mandarachal alone?
Lord Vishnu said, ” Take help of Asuras and use them to achieve your end, but REMEMBER you must be careful, however, not to desire any of the things that come out of the ocean and to give vent to anger if any of those things are forcibly taken away by asuras.”
“But what about the nectar, if Asuras took away that from us?” asked devtas. Lord Vishnu assured them that Asuras will not get the nectar. Convinced Brahma ji returned to his abode while Indra & devtas went to meet BALI ( King of Asuras).
Seeing Indra unarmed and helpless Asuras ran towards him but Bali shouted,”No, let’s wait.Perhaps devtas have come with a proposal that might be worth our while.” Bali received Indra & other devtas with respect. Indra told Bali about their mission of arrival and requested them (Asuras) to forget the fight and work together to achieve the task.
In return they decided to equally share nectar of immortality that would be created by churning. Bali & his chiefs favored the proposal and peace was declared between them and they (Asuras) suggested that let’s not waste time and begin the task immediately.
Mount Mandarachal was needed as a churning rod. Strong warriors made efforts with their hordes in uprooting the mountain and carrying it to the ocean. But they barely had covered half the distance and they got tired and the mighty mountain fell, crushing large numbers of Devtas & Asuras under it. Seeing this Indra prayed to Lord Vishnu for his help.
Lord Vishnu came on Garuda (his mount) to save the Devtas. Lord Vishnu brought mountain Mandarachal to the ocean with the help of Garuda. When mountain was placed in the ocean Vasuki came at the scene to play his role. Lord Vishnu addressed him by saying, “Play your role & you shall receive your share of nectar. The jagged surface of Mount Mandarachal will not hurt you at all.”
Reassured Vasuki rounded himself around the mountain. With full of joyous anticipation Devtas & asuras started churning the ocean. But their joy soon turned into despair, as the heavy Mount Mandarachal, which had no support at the bottom started to sink in the ocean.
Lifting it out was a great problem. Devtas requested Vishnu once again for help and Vishnu said, “I’ll take a form of kurma (a tortoise) and hold the mountain on my back until the ocean is fully churned and nectar is obtained.” Vishnu became a tortoise and held the mountain on his back.
At this point Indra tricked asuras by asking them to stay on the tail side of Vasuki serpent while churning the ocean. But Asuras suspected foul play in this and they themselves choose to be on the head side and told devtas to hold the tail side.
Soon Asuras learned that they have been deceived by Devtas as the poison coming from Vasuki’s mouth was weakening them. So to save themselves from this poison they began churning the ocean faster and this forceful churning first threw up the deadly poison HALAHAL, which was the concentrate of all the impurities from the ocean. Its poisonous fumes choked all the humans, Devtas & Asuras.
Frightened at this few Devtas ran to Lord Shiva at Mount Kailash for help. God assured them that they need not to fear as he will drink the poison. Lord Shiva collected the poison and swallowed it.
Once all the poison was removed from ocean, devtas & Asuras resumed churning the ocean. As they continued churning fourteen magnificent treasures emerged from the ocean**, but Amrit (nectar) was no were in sight. Both the Devtas and Asuras were losing their patience. And finally from the ocean bed emerged- Dhanvantari with a pot of nectar in his hand.
Seeing this Asuras ran towards Dhanvantari & grabbed the pot of nectar from him and started fighting regarding who would take possession of that pot. Devtas watched this in dismay. But remembering Lord Vishnu’s command that they should not quarrel over whatever comes out of the ocean, they made no move. Vishnu became very pleased with devtas. He told Devtas, “Don’t be dejected, the greed of nectar has already divided Asuras and now I shall charm them with my powers & give you the nectar.”
Vishnu disguised himself as apsara – Mohini ( the most beautiful women) and approached asuras. Asuras forgot about the nectar as they were mesmerized by her beauty.
“Who are you, beautiful lady?”, asked King Bali.
Mohini smiled and replied in a melodious voice, “I’m Mohini and I have come to distribute this amrit among all of you.”
They were prepared to do anything she said. Vishnu, in the form of Mohini, said to them, “You must do as I ask you to do.” So infatuated were the Asuras that they entrusted the jar of nectar to her.
Mohini then said to the Asuras that, “I will do so if you don’t question my actions.” Not knowing who she really was they agreed to her proposal. She then instructed, “Go ahead take bath & assemble in a row, Asuras in one row & devtas in the other row.”
When they had all assembled Mohini began serving nectar to Devtas first. Seeing this Asuras thought, “Mohini would be displeased unnecessarily if we object to it.”
Mohini kept asuras under her spell and she finished the pot of nectar by giving the whole nectar to the devtas. But one of the Asura was watching this and thought something is fishy. He quietly sneaked into the rows of devtas and received his share of nectar. But before he could gulp it down Devtas identified him and Lord Vishnu in the form of Mohini threw his Sudharsan Chakra and killed him.
Devtas were filled with energy and the curse of Saint Durvasa was lifted. Mohini then assumed her original form- form of Lord Vishnu. Asuras were surprised to see this as they had been deceived and there was no nectar left for them. After finishing his task Lord Vishnu flew away on his Garuda.
The furious Asuras declared war with devtas. Devta- Asura war on the seashore was a terrible one but Devtas who had drank nectar of immortality fought with asuras and drove them away.
In this avatar Lord Vishnu revived the lost glory of those who were gentle and sought refugee in him and punished those who were aggressive and had no faith in him.
**Fourteen Treasures that came out of the ocean during churning were –
FOURTEEN TREASURES DESCRIPTION 1. Wish-fulfilling tree Kalpavriksha. Its branch bore every kind of fruit and flowers one wished for. 2. Wish-fulfilling cow Kamadhenu. The sages decided to take care of it. Its udders produced enough food to feed the whole universe. 3. Wish-fulfilling gem Chintamani. Some say Vishnu placed it on his crown. Others say that the Nagas (serpents) hid it, fact not exactly known. 4. Seven-headed flying horse Ucchaishrava. Bali, leader of the Asuras, took possession of this horse. 5. Six-tusked elephant Airavata. Indra made this beast his mount. 6. Conch - Panchajanya. The sacred Shankh. 7. Bow of king Saranga. It was given to the kings of earth. 8. Beautiful nymph Rambha. She knew how to pleasure the senses in 64 different ways. She won Indra's heart so he carried her off to Amravati, radiant city of Devtas. 9. Moon-god, Chandra. Every woman fell in love with him. He cast the spell of romance across the universe. 10. Goddess of wine Varuni. She became the wife of Varuna, the ocean-god, and was loved by all creatures. 11. Physician Dhanvantari. An incarnation of Vishnu, the enemy of disease, he brought with him Ayurveda, the science of healing and AMRIT (NECTAR). 12. Goddess of fortune Sri. Everybody wanted to marry her, but she chose Vishnu. She placed Vaijayanti, the garland of eternal victory, around his neck. 13. Elixir of immortality Amrita. Asuras stole this much-sought-after drink. Vishnu, in form of enchantress Mohini, bewitched the demons so that while they admired her beauty, she poured the drink down the throats of Devtas. 14. Poison Halahal. Nobody wanted this lethal liquid. So Shiva drank it. The poison turned his neck blue and he is also known as NEELKANTH.
*Story behind this curse- Once Saint Durvasa – a short tempered saint by nature, offered garlands of beautiful flowers to Lord Indra-the king of Gods. But proudly he passed it to his elephants who carelessly trampled it all. Enraged by this, Saint Durvasa cursed Indra and as of a result of this curse all the devtas became weak.