Arunachala, if one is silent only by restraining from speech, sits like a rock without blossoming, but is without the clarity stemming from the experience of the natural state of stillness, is that silence called stillness?
Submerging in the stillness emanating from swaroopa anbhuvam (literally ‘form experience’) is true stillness. When the heart-knot is broken, and body-identification is destroyed, the resulting pure silence is the true state of stillness. For the gnani absorbed in such stillness, no desire or resolve arises unless impelled by divine will.
The one who is established in the silence of equanimity (stitha pragnan) without any sense of doership (karthuthva), is not disturbed by anything. Peace comes from the silence of the mind not merely the silence of the tongue.
TRK quotes a verse by Thaayumaanavar in this regard (‘sithamounam seyal vaakelamuvum maounam)
My note: However, stillness of speech is recommended as a first step to stillness of being by Adi Shankara in this verse quoted by Periyava:
Yogasya prathamam dwaram vangnirodho.parigraha: /
Nirasha cha niriha cha nityamekantasheelata
(The main entrance to the kingdom of yoga lies in stopping speech/words - http://dharmakirtan.blogspot.com/2012/11/yogasya-pratamam-dwaram-vaang-nirodha.html)
MahaPeriyava often went into kaaashta mounam where kaashtam means firewood, without any movement whatsoever. You can read more on this topic in Deivathin Kural Part 3.