Jnana Yoga-Bhagavad Gita Chapter 4 [Approaching the Ultimate Truth]
Krishna Said > Shaloka: 29
And there are even others who are inclined to the process of breath restraint to remain in trance, and they practice stopping the movement of the outgoing breath into the incoming, and incoming breath into the outgoing, and thus at last remain in trance, stopping all breathing. Some of them, curtailing the eating process, offer the outgoing breath into itself, as a sacrifice.
All these performers who know the meaning of sacrifice become cleansed of sinful reaction, and, having tasted the nectar of the remnants of such sacrifice, they go to the supreme eternal atmosphere.
This system of yoga for controlling the breathing process is called pranayama, and in the beginning it is practiced in the hatha-yoga system through different sitting postures. All of these processes are recommended for controlling the senses and for advancement in spiritual realization. This practice involves controlling the air within the body to enable simultaneous passage in opposite directions. The apana air goes downward, and the prana air goes up. The pranayama-yogi practices breathing the opposite way until the currents are neutralized into puraka, equilibrium. Similarly, when the exhaled breathing is offered to the inhaled breathing, it is called recaka. When both air currents are completely stopped, it is called kumbhaka-yoga. By practice of kumbhaka-yoga, the yogis increase the duration of life by many, many years. A Krishna conscious person, however, being always situated in the transcendental loving service of the Lord, automatically becomes the controller of the senses. His senses, being always engaged in the service of Krishna, have no chance of becoming otherwise engaged. So at the end of life, he is naturally transferred to the transcendental plane of Lord Krishna; consequently he makes no attempt to increase his longevity. He is at once raised to the platform of liberation. A Krishna conscious person begins from the transcendental stage, and he is constantly in that consciousness. Therefore, there is no falling down, and ultimately he enters into the abode of the Lord without delay. The practice of reduced eating is automatically done when one eats only Krishna-prasadam, or food which is offered first to the Lord. Reducing the eating process is very helpful in the matter of sense control. And without sense control there is no possibility of getting out of the material entanglement.
From the foregoing explanation of different types of sacrifice (namely sacrifice of one’s possessions, study of the Vedas or philosophical doctrines, and performance of the yoga system), it is found that the common aim of all is to control the senses. Sense gratification is the root cause of material existence; therefore, unless and until one is situated on a platform apart from sense gratification, there is no chance of being elevated to the eternal platform of full knowledge, full bliss and full life. This platform is in the eternal atmosphere, or Brahman atmosphere. All the above-mentioned sacrifices help one to become cleansed of the sinful reactions of material existence. By this advancement in life, one not only becomes happy and opulent in this life, but also, at the end, he enters into the eternal kingdom of God, either merging into the impersonal Brahman or associating with the Supreme Personality of Godhead, Krishna.