In Chapter 17 of the Bhagavad Gita, Sri Krishna describes the tamasic, rajasic and sattwic types of tapas, austerity. Sattwic austerity or self-discipline is expressed through the body, speech and mind.
Devadwijagurupraajna poojanam shauchamaarjavam;
Brahmacharyamahimsaa cha shaareeram tapa uchyate.
Worship of the gods, the twice-born, the teachers and the wise, purity, straightforwardness,
celibacy and non-injury - these are called the austerities of the body. (14)
Using the feet in pilgrimage to sacred temples, using the hands in cleaning the temples, in collecting materials for worship of God, service to parents, preceptors, the poor and sick is called physical austerity. Non-stealing and not coveting are also included. Immense musing on the objects of the senses does more harm to the inner spiritual life than actual sense gratification. If the mind is not rendered pure by sadhana, mere mortification of the external senses will not produce the desired effect.
The senses always have an outgoing tendency. The mind operates through the senses. Control of the one goes hand in hand with the other. Control of the senses is also control of the mind, because the mind is a bundle of senses only. There is no mind without senses.
Just as an enemy can be easily conquered if you have a two-pronged attack, so also the mind can be controlled easily if you attack it in two fronts simultaneously – an external attack on the senses and an internal attack on the mind itself by the eradication of the desires.
Anudwegakaram vaakyam satyam priyahitam cha yat;
Swaadhyaayaabhyasanam chaiva vaangmayam tapa uchyate.
Speech which causes no excitement is truthful, pleasant and beneficial,
and the practice of the study of the Vedas, are called austerity of speech. (15)
The words of the man who practises the austerity of speech cannot cause pain to others. His words will bring cheer and solace to others. His words prove beneficial to all. The organ of speech causes great distraction of mind. Control of speech is a difficult discipline but you will have to practise it if you want to attain supreme peace. Nothing is impossible for a man who has a firm determination, sincerity of purpose, iron will patience and perseverance. It is said in the Manu Smriti:
Satyam bruyaat priyam bruyaat na bruyaat satyampriyam
Priyam cha naanritam bruyaat esha dharma sanaatanah.
One should speak what is true; one should speak what is pleasant.
One should not speak what is true if it is not pleasant nor what is pleasant if it is false. This is Sanatana Dharma.
To be an austerity, speech must form an invariable combination of all four attributes mentioned in this verse, such as non-excitement or non-painful, truthful, pleasant and beneficial. If it is wanting in one or the other of these attributes, it cannot form the austerity of speech. Speech may be pleasant, but if it is lacking in the other three attributes, it will no longer be an austerity of speech.
Manahprasaadah saumyatwam maunamaatmavinigrahah;
Bhaavasamshuddhirityetat tapo maanasamuchyate.
Serenity of mind, good-heartedness, purity of nature,
self-control—this is called mental austerity. (16)
Just as a lake which is without a ripple on its surface is very tranquil, so also the mind which is free from modifications, from wandering thoughts of sensual objects, is quite serene and calm. Mouna is the result of the control of thought as far as it concerns speech, silence of the mind, the ability to remain calm even amidst disturbing factors from without. Purity of nature means honesty of purpose, freedom from cunningness when dealing with other people. It is the pure state of the mind wherein there is absence of lust, anger, greed, and so on.
Shraddhayaa parayaa taptam tapastattrividham naraih;
Aphalaakaangkshibhiryuktaih saattwikam parichakshate.
This threefold austerity practised by steadfast men with the utmost faith,
desiring no reward, they call sattwic. (17)