Tapas - burning zeal, heat, is one of the 5 niyamas of yoga.
The yamas (ahimsa, satya, asteya, bramacharya and aparigraha) teach us how to relate harmoniously in society.
The Niyamas (saucha, santosa, tapas, svadyaya and Ishvara Pranidana) teach us how to grow in a balanced and harmonious way as individuals.
I have first hand experience of the power of tapas -burning heat - fire.
The two early gods in Hindu mythology are the god of fire (Agni) and the god of wind (Vayu). Fire and Wind.
I couldn't breathe a few days back. Vayu - the god of wind - was weak in me. I needed fire (Agni) - heat - expresed in the act of tapas - sweat - to burn the bug out of my system to be able to breathe again. The transforming power of heat can heal and destroy - that is why it must be respected.
Balancing the pairs of opposites is what yoga is all about. Fire and Wind may or may not be considered opposites - but they do have a relation to one another. Fire cannot burn without wind (air). And if a person can't breathe - the heat leaves their body.
How strongly does the fire burn in you?