The only means of authentic spiritual communication is the interior speech which is uttered in the silence from which the Word emerged, and which is only heard in the silence.
~ Abhishiktananda
Breathing is one internal function that the conscious mind can control with comparative ease. The effect of controlled breathing is almost like communication with all conscious parts of one's being saying to them, "Simmer down and listen; there is something beyond the turmoil". It is communication in action that often works when words merely go in one ear and out the other, not even changing the cognitive mind. In essence, the effect is to turn all the elements of our will toward stillness and waiting.