Samudra Manthan

In Hinduism, Samudra manthan (Devanagari: समुद्र मंथन) or the churning of the ocean of milk is one of the most famous episodes in the Puranas and is celebrated in a major way every twelve years in the festival known as Kumbha Mela.
According to legend, during the Samudra Manthan a pot of poison emerged from the ocean. This terrified the gods and demons as the poison was capable of destroying the entire world, and they ran to Shiva for help.
Thence, bursting like a mighty flame,
A pestilential poison came,
Consuming, as it onward ran,
The home of God, and fiend, and man.
Then all the suppliant Gods in fear
To S'ankar, mighty lord, drew near.
To Rudra, King of Herds, dismayed,
'Save us, O save us, Lord!' they prayed.
Then Vishnu, bearing shell, and mace,
And discus, showed his radiant face,
And thus addressed in smiling glee
The Trident wielding deity:
What treasure first the Gods upturn
From troubled Ocean, as they churn,
Should--for thou art the eldest--be
Conferred, O best of Gods, on thee.
Then come, and for thy birthright's sake,
This venom as thy firstfruits take.'
He spoke, and vanished from their sight.
When Siva saw their wild affright,
And heard his speech by whom is borne
The mighty bow of bending horn, 1b
The poisoned flood at once he quaffed
As 'twere the Amrit's heavenly draught.
Then from the Gods departing went
S'iva, the Lord pre-eminent. (Ramayana/CANTO XLV)
To protect the world from its evil effects, Shiva drank the deathly poison but held it in his throat instead of swallowing it. Because of it, his throat turned blue, and he was given the name Neelakantha, the blue-throated one. Shivaratri is the celebration of this event by which Shiva saved the world.

Maybe, the story represents the spiritual endeavor of a person to achieve self-realisation through concentration of mind, withdrawal of senses, control of desires and practice of austerities and asceticism.

• The Devas and Asuras represent the positives and negatives respectively of one's personality. The participation of both the Devas and the Asuras signifies that when one is seeking bliss through spiritual practice, one has to integrate and harmonise both the positive and negative aspects and put both the energies to work for the common goal.
• The ocean of milk is the mind or the human consciousness. The mind is like an ocean while the thoughts and emotions are the waves in the ocean.
• Mandhara, the mountain symbolises concentration. The word Mandhara is made up of two words Mana (mind) and Dhara (a single line) which means holding the mind in one line. This is possible only by concentration.
• Mount Mandhara was upheld by Lord Vishnu as a Kurma (tortoise). The tortoise here symbolises the withdrawal of the senses into oneself (just as a tortoise withdraws its head into its shell) as one practices mental concentration and meditation or contemplation.
• Vasuki symbolises desire. Vasuki used in the churning of the ocean denotes that the Devas and the demons held desire (to seek immortality) as a rope and churned the mind with the help of concentration and withdrawal of the senses. Desire, if not controlled will overpower and destroy an individual.
• The Halahala poison symbolises suffering and pain (counter-reaction of the mind and body) that one undergoes at the beginning of spiritual sadhana (practice). When the mind is subjected to intense concentration, the first thing that comes out of the process is intense suffering and great inner turmoil. These must be resolved otherwise further progress is not possible.

Though interpretation is always opened...

OM NAMAH SHIVAYA