What is Tapasya? What is concentration?

The following is an excerpt from a samvaad (dialogue) session with Acharya Prashant.

Question 1: What is ‘Tapasya‘ (austerity)? Why is ‘Tapasya‘ necessary?

Acharya Prashant (AP): In the cold areas of the country, it becomes important, especially in winters, to let the sunlight in. Quilts etc. are kept out in the open so that they receive the Sun treatment. The Sun must beat down on them.

The ‘taap’(heat) of the Sun removes a lot of impurities.

That is ‘tapas’.

Feel the heat. Feel the heat.

Listener (L): I still don’t get it.

AP: You know where the heat is, you know where the Sun is. Face it! There are many ailments for which you require heat treatment, or you require exposure to UV rays emitters. What do you do? You just bring yourself to the heat-emitter and stand in front of it, naked. You allow the heat to bake you, roast you, cleanse you.

There was a man, who once had few microbes, little germs, bacteria, on his skin. The doctor told him that sunlight kills these germs, or at least makes them run away. The germs overheard the doctor’s advice.

So, when the man was gleefully returning to his house, preparing to try the heat treatment, the ‘tapas’, the germs said, “You…