The"Panchaksharam"(Namashivaya) contains a lot of importance in life of the devotees.
Sivarathri vow also has a legendary story line of its own. It's the story about a King named Chitrbhanu who belonged to the Soorya race and was the emperor of Jambu kingdom. The story underlines a debate that took place when Astavakra Maharshi. Was calling on King Chitrabahnu. In his previous birth, the king was a hunter and one night he was caught in a huge jungle. Due to fear of wild animals he sought shelter on a treetop. To drive away the animals that threatened his life he threw down the branches and leaves of the tree. Next day morning, he collected his goods and went back to his hut. Years passed by, the hunter grew old and died. When the soldiers of Yaman came to carry away his soul, he pleaded his case being a devotee of Lord Siva and was thus taken to Kailas. On seeing him, Lord Siva remembered him and blessed him with all prosperity and abundance in the next life. The reason behind this blessing was that the night that he had suffered in the jungle years back was Sivarathri, he was without food and the tree on which he sought safety was a koovala tree. It was onto a Sivalingam that these leaves fell. This pleased Lord Siva immensely. If the unknown piety of a human could usher in so great a result, how much more would Lord bestow to his faithful devotees.

Yet another legend exists behind the greatness of Sivarathri. Mahadev had to consume the poison "halahala" to save the world. To prevent the poison affecting Him, all the deities and devotees fasted and prayed. It is the result of this that the poison went unharmed and stayed in the Throat of Lord Siva.