Long ago, the devtas and the asurs decided to churn the Ksheer Sagar, the ocean of milk, together. They wanted to bring out amrit, the nectar, from deep inside the ocean. Mount Mandarachal was used as the churning stick, and Vasuki the serpent became the rope. Bhagwan Vishnu took the form of a turtle, called the Kurma avatar, and held the mountain on his back so that it would not sink.
The devtas pulled Vasuki from one side and the asurs from the other. The ocean began to swirl round and round. But before the amrit came out, a terrible poison rose from the ocean. It was called Halahal. Its heat and fumes began to spread everywhere. Trees and plants, animals and birds, devtas and asurs, everyone was frightened. It felt as if the whole world was in danger.
Everyone rushed to Shiv ji on Mount Kailash. With folded hands they said, "O Mahadev, please protect us. This poison has put everyone in danger."
Shiv ji is very kind. He looked at Maa Parvati and said, "When everyone is in trouble, the one who has the strength must step forward." Maa Parvati knew her husband's power. Calmly, she agreed.
Shiv ji took the poison in his palm and drank it. But he did not let it go down past his throat. He held it right there in his throat. Because of the poison, his throat turned blue. From that day, Shiv ji has been called "Neelkanth", the one with the blue throat.
Once the poison was gone, everyone breathed a sigh of relief. The devtas and asurs began churning again. Now, one by one, many precious treasures came out of the ocean: Kamdhenu the wish-giving cow, Airavat the elephant, the Kalpavriksha tree, Maa Lakshmi, and at last Bhagwan Dhanvantari, carrying the pot of amrit.
All the devtas cheered for Shiv ji. They said, "Mahadev, you took pain upon yourself for the good of all." Shiv ji only smiled and sat down to meditate again.
People say that the devtas poured water over Shiv ji to cool the heat of the poison. That is why, even today, devotees lovingly offer water on the Shivling and say "Har Har Mahadev".
The lesson Stepping forward to help others is the greatest goodness.
Source: Bhagavat Purana, Skandh 8, Adhyay 7 (retold); also told in the Valmiki Ramayan, Bal Kand, sarga 45
