Om namah shivay
This threefold austerity, practiced by steadfast men with the utmost faith, desiring no reward, they call sattvika.
The austerity which is practiced with the object of gaining good reception, honor and worship, and with hypocrisy is here said to be rajasa, unstable and transitory.
That austerity which is practiced out of a foolish notion, with self-torture, or for the purpose of destroying another, is declared to be tamasa.
It is strange that even the three types of austerity (of body, speech and mind) can be practiced in a rajasa or tamasa way! – though the words “This threefold austerity” may apply only to the first verse and the other two may allude to other forms of austerity – in which case the meaning is abundantly clear and simple.
The most noble deeds can be performed hypocritically, but the effect will be the very opposite of what is desired. There is, however, a saving feature in such hypocritical good work and austerity – they are “unstable and transitory.” Hypocrisy has been unequivocally condemned in all our scriptures, but it has always existed. Hypocrites have their little day! It is true that their magic spell ends soon, but not soon enough to minimize the havoc caused. The genius of the hypocrite uses a noble garb and sometimes it is impossible to detect him before he has achieved his purpose, though this is always a short-lived one. Let us be thankful for small mercies!
The third category is an allusion to the demoniacal type of austerity. It is difficult to see how it can satisfy the standards of the austerity of mind mentioned in verse 16. There is, however, no limit to the perversions of the tamasa or deluded mind that can always interpret scriptures in its own way!
~~ Swami Venkateshananda