The importance of the breath in the body is like the influence of the weather in the world. As the body and mind act and react on one another, so the influence of the breath takes the chief place in directing mind and body both. Every emotion is caused by the breath flowing in a certain direction, also the degree of the force of the breath.

There are three different rhythms of breath which have influence upon the mind.

Slow breath gives tranquility to the mind, and all the creative faculties of mind have scope of work given by this rhythm.
Moderate breath helps the mind to continue its activities. If one wanted to make out a plan of work, or wished to accomplish a certain work, the slow activity of breath spoken of above would not be helpful; though for poetry or music the activity of breath which is slow is more helpful.
But quickness in the rhythm of breath produces confusion, although it gives a force to physical activities. One can run better or swim well when the breath is in fairly quick rhythm. When the rhythm of the breath is too quick, it brings confusion to the mind and exhaustion to the body.

One who does not breathe fully, in other words freely and deeply, can neither be well physically nor make use of his mental faculties. Very often one finds most learned and intelligent people unable to work as they wish and incapable of finishing a work which they have taken up. Sometimes a person thinks it a bodily weakness or mental weakness or lack of enthusiasm or loss of memory, not knowing that it is very often a matter of regularizing the breath. Most often people think that it is the external senses being tired or exhausted that prevents their thinking, but in reality it is the absence of right breathing, for right breathing can make the mental faculties clearer and the outer organs of the senses more capable of perceiving.

This shows that the mind can live a fuller life by what I call full breath. For a Sufi, therefore, breath is a key to concentration. The Sufi, so to speak, covers his thought under the breath. This expression of Rumi's I would interpret that the Sufi lays his beloved ideal in the swing of the breath. I remember my Murshid's saying that every breath which is inhaled with the consciousness of the Divine Beloved is the only gain, and every breath inhaled without this consciousness is the only loss there is.