Once when everything in all the worlds got reduced into Lord shiva, in that darkness of nothing present, the mother Parvati worshipped Lord shiva in the Agamic way with great devotion. The parameshwar pleased by Her prayer blessed Her. She asked for the benefit of all the creatures that in future whoever worships the Lord on the shiva ratri day with devotion, they should be blessed and should be given the ultimate liberation. The pashupati granted that showing way for all of us to get blessed easily.
When Brahma and Vishnu fought between themselves as “who is the greatest”, Lord Shiva appeared before them as a pillar of fire. They were not able to find the starting and end of that pillar. This day is Thirukkaarthikai.
Then Brahma and Mahavishnu repented for their mistake and prayed to Lord Shiva for forgiving their sin worshiping the shiva lingam which is the form of the flame. In the night of Shiva rathri Lord Shiva appeared before them and blessed them. Devotees pray the God throughout the night of Shiva rathri by performing Abisheka, chanting and other holy deeds.
Every month in Krishna paksha chathurdhasi (fourteenth moonday) is called masa Shiva rathri. The one that comes in the month of “Masi” (mid February to mid March) is called Maha Shiva rathri. This is considered as the most important vrata by the devotees.
There are many incidents told about the greatness of this day. Once a hunter in a jungle after searching throughout the jungle, was quite tired and could not get any animal. In the nightfall a tiger started chasing him. to escape from that he climbed a tree. That was a Bilva tree. The tiger sat under the tree waiting for him to come down. The hunter who sat on a branch of the tree was quite tense and didn’t want to sleep. He was plucking the leaves and putting down as he was not able to be idle. Below the tree there was a Shiva lingam. The whole night went on like this. God was pleased with the Upavasa (hunger) and the Pooja the hunter and the tiger did even without knowledge. He is the peak of the grace. He gave the hunter and the tiger “Moksha”.
In a Shiva temple on a Maha Shiva rathri day the lamp kept in the altar was very dim. That time a mouse which came take its prey touched the flame. Due to the heat it moved its head immediately. In the process it kindled the lamp and the altar was illuminated well. Lord Shiva, pleased by this deed made the mouse Mahabali, the renowned asura king.
There are many incidents like this told in our Puraanas. If we do the vrata with pure devotion and love there can be no doubt about getting the Grace of the Almighty.