From Hatha yoga pradipika with Hans Ulrich Rieker commentary -Quote 6

"There are 72,000 nadis in this cage [body]. Sushumna is the central nadi which contains the
shabhavi shakti. This has the property of bestowing bliss upon the yogi. All others are then useless.
−−Guide the prana into the sushumna and kindle the gastric fire and awaken the kundalini. Only

when prana fiows through the sushumna wilt there be samadhi. All other methods are futile. When
breath is suspended then [discursive] thinking also is suspended. He who has power over his mind
can also control prana.
[For] the two causes that activate the mind are prana [respiration] and the sources of karma
[vasanas, latent tendencies]. Death of one [of these] is the death of the other. When mind is
absorbed, breathing subsides: when prana is absorbed in the sushumna [not available to the body]
then mind also is absorbed."

The deepest sense of this yoga will be understood only by one who is convinced that from physical
process to psychological experience and religious phenomena there is one straight (if usually secret)
path, and that none of the three can exist and function by itself. He who is prepared to familiarize
himself with what naturally seems to be a strange terminology will find not only confirmation of the
most modern knowledge, but the possibility of new insights as well, for the problem of relationship
between the inner and outer worlds will always be a
topical one as long as the human race exists. The last word on it can never be expected, for each
culture, even each phase of individual life presents new perspectives. It is by the great visionary
works of antiquity that we are most deeply touched−− we who have become so clever.

"Mind and prana are related to each other like milk and water. If the one dries up the other one
also dries up. In whatever chakra the prana is concentrated mind becomes fixed, and where the mind
is fixed prana is conquered"

The fact that men's cultural levels differ so greatly is not simply a problem of society; nor does it
depend on ambition, or even on intelligence. It is really the chakras that cause stratification in
culture.
Genius is the product of the highest development potential of that chakra by which it lives. As long
as our mind is not nourished by that same chakra we only comprehend the lower levels. At the
highest level our understanding is no longer limited. There we need no intellectual hints; we perceive
the spirit everywhere, even in silence.
The chakra determines whatever level of development we are on, and this level determines the measure of our consciousness.