Verse 16 in chapter 17 of the Bhagavad Gita talks about austerity and serenity of mind. (Chapter 17, Verse 16)
Serenity of mind, good heartedness, silence, self-control, purity of nature – these together are called ‘mental austerity.’
Serenity of mind can be gained only when our relationship with the world at large is put on a healthy basis of understanding, tolerance and love. Further, one who is an uncontrolled sensualist can have little serenity or composure.
The mind runs out through the sense organs into the sensual fields to eke out its satisfaction. The driving force that sets the mind on its endless errands is an intellect ever seething with desires.
Quietude of the mind can be gained only when it is protected from both the inflow of stimuli from the tempting sense objects of the outer world and the whipping desires that march out from the intellect to drive the mind out into the fields of enjoyment.
One who has discovered for himself a divine ideal – in the contemplation of which his mind forgets to run about, or his intellect overlooks to send out new desires – alone can hope to win serenity of the mind.
(Source: Holy Gita – Ready reference – Published by Chinmaya International Foundation)