=Importance of Control of Speech=
To control the eye is good; to control the ear is good; to control the nose and the tongue is good.
The man who is master over his hands, his feet and his tongue, who controls himself wholly, who delights in meditation, who is calm and leads a solitary life, can be called a Bhikkhu. <ref>https://incarnateword.in/cwm/03/the-bhikkhu#p1-p3</ref>
Calm in action, calm in speech, calm in mind, serene, emptied of all earthly appetites, this Bhikkhu is called "The Serene One". <ref>http://incarnateword.in/cwm/03/the-bhikkhu#p19</ref>
Yes, control of the speech is very necessary for the physical change.
The question of mental austerity immediately brings to mind long meditations leading to control of thought and culminating in inner silence. This aspect of yogic discipline is too well known to need dwelling upon. But there is another aspect of the subject which is usually given less attention, and that is control of speech. Apart from a very few exceptions, only absolute silence is set in opposition to loose talk. And yet it is a far greater and far more fruitful austerity to control one's speech than to abolish it altogether.<ref>http://incarnateword.in/cwm/12/the-four-austerities-and-the-four-liberations#p33</ref>
Not to allow the impulse of speech to assert itself too much or say anything without reflection, but to speak always with a conscious control and only what is necessary and helpful.<ref>http://incarnateword.in/cwsa/31/speech-and-yoga#p38</ref>
... speech and the five senses of knowledge are the instruments of the mind. Prana, the life-force in the nervous system, is indeed the one main instrument of our mental consciousness; for it is that by which the mind receives the contacts of the physical world through the organs of knowledge, sight, hearing, smell, touch and taste, and reacts upon its object by speech and the other four organs of action; all these senses are dependent upon the nervous Life-force for their functioning. The Upanishad therefore begins by a query as to the final source or control of the activities of the Mind, Life-Force,Speech,Senses.<ref>http://incarnateword.in/cwsa/18/the-question-what-godhead#p1</ref>
Speech breaks out as the expression of the vital and its habits without caring to wait for the control of the mind; It is therefore this tendency that must cease in the vital itself. Not to be under the control of the impulse to speech...
===Vibration in Speech===
The habit of criticism—mostly ignorant criticism of others—mixed with all sorts of imaginations, inferences, exaggerations, false interpretations, even gross inventions is one of the universal illnesses of the Asram. It is a disease of the vital aided by the physical mind which makes itself an instrument of the pleasure taken in this barren and harmful pursuit of the vital. Control of the speech, refusal of this disease and the itch of the vital is very necessary if inner experience has to have any true effect of transformation in the outer life.
As for helping [others], you can only be sure of that if you yourself have an assured basis, with the psychic being always prominent, full of faith and joy and strength,—then others can gather strength and faith and joy from such a one by speech or contact. But to arrive at that you must, as I have been telling you, open yourself to the Light and Force that come from myself and the Mother and to no other influence.
"When a thought is expressed in speech, the vibration of the sound has a considerable power to bring the most material substance into contact with the thought, thus giving it a concrete and effective reality. That is why one must never speak ill of people or things or say things, which go against the progress of the divine realisation in the world. This is an absolute general rule. And yet it has one exception. You should not criticise anything unless at the same time you have the conscious power and active will to dissolve or transform the movements or things you criticise. For this conscious power and active will have the capacity of infusing Matter with the possibility to react and refuse the bad vibrations and ultimately to correct it so that it becomes impossible for it to go on expressing itself on the physical plane.
==Role of Speech in Transformation==
The first condition of inner progress is to recognise whatever is or has been a wrong movement in any part of the nature,—wrong idea, wrong feeling, wrong speech, wrong action,—and by wrong is meant what departs from the Truth, from the higher consciousness and higher self, from the way of the Divine. Once recognised it is admitted,—not glossed over or defended,—and it is offered to the Divine for the Light and Grace to descend and substitute for it the right movement of the true consciousness.
...it would be better to get full control of the speech—it is an important step towards going inward and developing a true inner and Yogic consciousness.
The speech must come from within and be controlled from within.
...complete truth of speech is very important for the sadhak and a great help for bringing Truth into the consciousness. It is at the same time difficult to bring the speech under control; for people are accustomed to speak what comes to them and not to supervise and control what they say. There is something mechanical about speech and to bring it to the level of the highest part of the consciousness is never easy. <ref>http://incarnateword.in/cwsa/31/speech-and-yoga#p33</ref>
=How to Use Speech Effectively?=