This masik shivaratri here is a popular story from the Puranas.
There was once a poor hunter from Varanasi whose name was Suswara. Suswara would go to the forest and hunt whatever game came his way and thus feed his family. One day, he wandered deeper into the forest in search of more game. Soon darkness set in, and he turned to go home. Unable to find his way back, Suswara climbed a tree to be safe from the wild animals. Attracted by his scent, animals came lurking under the tree. Throughout the night the animals kept prowling beneath the tree.
Suswara was unable to get even a wink of sleep. He kept vigil throughout the night. He plucked leaves from the tree, which happened to be a Bilwa tree, and dropped them on the ground. Unknown to Suswara, there was a Shivalinga at the foot of the tree; and so, although he was unaware of it, by dropping the sacred Bilwa leaves, Suswara was making a sacred offering to the Shivalinga. That night happened to be Shivaratri. So, the hunter had unknowingly kept a night-long vigil and worshipped Shiva. Legend says that at the time of his death his soul became one with the lord.
Spiritual Significance of this story
The story above is an allegory. Just as the hunter sought to kill wild animals, the spiritual seeker tries to overcome lust, anger, greed, infatuation, jealousy, and hatred. The jungle is the mind where all these negativities roam about. A spiritual aspirant must kill these “animals” to be free. The name of the hunter was Suswara, which means “one of melodious voice”. This indicates the purity of intent and speech, which, in turn, imply a level of mental purity.
The hunter was born in Varanasi. Vara refers to the forehead while nasi is the nose. The point where both meets is Varanasi, in other words, the point midway between the eyebrows. This point is also called the Ajna chakra and is regarded as a nexus of the three Nadis: ida, pingala and sushumna. A spiritual aspirant who concentrates his or her mind on this point gains concentration and gradual control over his senses. The killing of the animals thus indicates control over one’s vasanas [latent tendencies]. The Bilwa tree corresponds to the spinal column. The tree’s leaves are special: each stalk has three leaflets. The three leaflets represent the three Nadis mentioned above. Keeping awake is symbolic of the kind of awareness and oneness of purpose that a spiritual aspirant needs to reach the goal. He cannot afford to be slack even for a moment. Shiva is the Supreme Consciousness that illuminates the three states of waking, dreaming and deep sleep. Offering the threefold Bilwa leaves to the Shivalinga heralds the return to a level of consciousness beyond the three states, which is the fourth state, Turiya. The dawning of that state is consonant with the awakening of the individual.