When Lord Vishnu in the guise of a maid bewitching grace and undertook to distribute the elixir among the Devas and Asuras, he decided to deny the Asuras and fed only Devas. Rahu was the Asura who understood the intention of Vishnu. He transformed himself into the form of Deva and stood among Devas. But Suriyan and Chandran detected this subterfuge of Ragu and intimated Lord Vishnu of Rahu’s maleficient cunning. But Lord Vishnu knew this only after he had already given Rahu the Elixir. Rahu had just then taken a mouthful, when Lord Vishnu hit him at the head. But Rahu had tasted the elixir and was now immortal. The dismembered head became Rahu, and the headless body Kethu. In revenge the dark snake that is Rahu grips Chandran and causes lunar eclipse. Kethu who is a red snake grips Suriyan and causes solar eclipse. Kethu by grace of Lord Siva became a Graha. His form became divine and he had the five heads of snake grown upon him. His consort is Chitralekha.
It is Kethu who determines as to whether an individual attains Moksha or not. The period of kethu’s influence is 7 years. To ensure that one has progeny, for the dawning of wisdom, to own a house one should worship lord Vinayaka, give the gem stone vaidooryam as a gift, recite verses on Machavatharam and worship at the shrine of Kethu.
Kethu gives wisdom, moksha, makes one live well, grace one with good children, bless one with chance to live in a foreign nation. He cures leprosy, fever, and tuberculosis and skin diseases.
The temple faces east and is surrounded by high walls on all four sides. There is the holy tank Nagatheertham in front of the temple and on its eastern side is an Arasa tree, on its western edge the Neem tree. There are snake’s images worshipped under the neem tree. The Asuras who were enraged at being denied the elixir for which they strove hard, tore the snake Vasugi which they had used as a rope for churning the ocean of milk and strew its pieces all over the bamboo forest.
The snake, whose life had not yet ebbed, grew up from the tail and when it came to know that Lord Siva had taken its poison into him, it asked to be forgiven and did penance. Lord Siva was pleased with Vasugi and manifested to her and asked her to seek a boon. The snake requested that Lord Siva should have his temple in the Bamboo forest itself and assist the grief of devotees who pray at this temple. The lord assented and is even now as Naganathaswamy showering his grace upon the unfortunate.
In the west end of the perambulatory route there are images of Vinayaka, Muruga with Valli and Deivanai, Mother Durga, Lakshmi, Narayanar, Maheshwari and Gajalakshmi for worship. In the last end of the route are the sanctums of Saniswarar, Bhairavar, Sambandar and Nagar. In the northeast facing west is the Kethu Bhagavan, his form divine, head in the form of a five hooded snake, his hands held together in front in a posture of worship. Naganathaswamy is to be prayed after worshipping Nandhi in the Silver enterance. There are also excellent statues of Natarajar, Kethu and other deities. Mother Soundaranayaki is in the great hall facing south.