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.
Just sit there right now
Don't do a thing
Just rest
For your separation from God
Is the hardest work in this world
Let me bring you trays of food
And something that you like to drink
You can use my soft words
As a cushion for your head
The small man
Builds cages for everyone
He
knows.
While the sage,
Who has to duck his head
When the moon is low,
Keeps dropping keys all night long
For the
Beautiful
Rowdy
Prisoners.
~ from THE GIFT by Hafiz, translated by Daniel Ladinsky