1. The left upper hand of Natraj holds the eternal fire. Although, The Natraj is surrounded by cosmic fire, he has immortal fire in his left hand. This is a transformational fire that represents the fire of cremation grounds that turns bodies into ashes. Lord Shiva is known to stay-in the cremation grounds as bhootnath. He applies the ashes on his body. By doing this, he accepts the mortal and immortal aspects of soul and merges them into himself. This fire also turns seawater into rain clouds. It is called the panch agni vidya. It works like this: 

2. When devotees offer milk, ghee, butter, water, curd to Shiva, he puts it into celestial fire or the dyulok agni and mixes it with somarus. He further offers this nectarine into parjanya agni that transforms into cloud and rains on earth. The water of the raindrops feeds bhumi agni to yield crops. These crops are consumed by men and offered to Purush agni. This Purush agni is then transformed by the male into the fire of female called Yoshita agni. By this panch agni vidya the offering given to god is transformed into the gift of life as offsprings of humans. This five fire process keeps the circle of life moving. 

3. Then again, the body is made of five tattva. The first two tattva, prithvi and jal, are refined through agni into the more refined tattva vayu and aakash.  

4. The fire at the hands of Natraj is also the fire of consciousness. In meditation, the energy that is coiled in the seven chakras undergoes the fire of consciousness, the forces get activated. These aroused forces lead to mindfulness and self-realization. 

5. Fire is considered the purest of all tattva. Every  other tattoo can be contaminated but not fire. Anything that passes through fire is purified. This is the reason why from age long time practice of havan is taking place. In Hinduism, the dead bodies of the human are offered in the fire. This is because the fire very quickly transforms the body into ashes. These ashes are the favorite of lord Shiva. He applies them all over his body. This act of the lord Shiva proves the purity of the ashes. 

6. The fire has a quality that it spreads fast. No matter how far it travels to the flames always move upwards, opposite to the gravitational pull from the earth. This is the power of wisdom. Wisdom spreads like fire. It spreads a long way and spread out. Even though, the popularity of a wise man moves in all directions a long way and spread out,  it only spreads in positive directions. The eternal agni in the hands of Natraj has a lot of specific meanings.