Dharanasu Ca Yogyata Manasah
Dharanasu = Intense concentration; Yogyata = capability; Manasah = of the mind; Ca = and.
Capability of intense concentration as well as the mind is achieved (by Pranayama).
The nature of mind is compared with flowing water. It is ever changing, ever stable. Keeps on moving. Therefore, it is difficult to hold the mind at one point, to concentrate. Even grown-ups, matured persons find it difficult to tame the forces of the mind.
An employee of a company could not pass the necessary examination for promotion to higher post because his mind would wander off, after studying half a page of the book. This is due to Rajasic nature, the speed of the mind.
There is a connection between the state of our mind and the flow of breathing. During an agitated moment, the breathing is fast. When deep relaxation, silence and peace take over, the breathing gets settled down. It becomes deep, soft and rhythmic.
Pranayama, featured by slow breathing, therefore, tames the unruly mind and makes it capable of performing Dharana.