The word Kriya is composed of two syllables, kri and yâ. In Sanskrit, kri means karma dhatu - action of the elements, and yâ means Soul or Atma. The word Kriya indicates action of the Soul or prâna karma. The first and most important action of the Soul is breath.
The word yoga comes from Sanskrit yuj which means union. The union of the individual soul with Spirit.
Kriya Yoga is a method to attain the union of breath and Soul in each inhalation and exhalation. Expressed in other words: the union of the individual soul with Spirit is called Kriya Yoga. This is true karma.
The practice of Kriya Yoga is based on breath, the brain and the spinal cord. Breath is the mediator between Soul and mind. The brain is the mediator between the sense organs and the mind. All our physical actions are reflected on our sense organs through the intermediary of the lower part of the brain located in the spinal cord. From this lower part of the brain where the lower mind is situated, we pass to the higher mind, then to breath, and lastly from breath to Soul (and then inversely).
The brain is connected to the mind and the mind is connected to chitta. Chitta (the higher mind) is composed of five actions, or five minds which have twenty-five qualities or natures, each creating two results which are called vrittis. This gives fifty types of different inner and outer results - fifty vrittis, which are manifestations of chitta. The vrittis are created by chitta, the higher mind, directly from the Soul through the means of breath. The object of yoga is to control the actions of chitta - Yogâshchittavrittinirodhah (Pâtanjali's Yoga Sűtra I, 2).
The mind is in constant motion. Our inner and outer actions change constantly and this is reflected by our breath. When we are afraid our breath is agitated, when we feel joy our breath is different, it is also different when we are angry or have any other type of emotion. When the breath is calm, the mind is calm. So, it is only through breath that we are able to control chitta and come to the state called nirodhah. Nirodhah means to close, to lock with a key - which means to stop all actions (vrittis) of chitta and thus have easy access to the meditation state of yoga. The control of chitta, stopping the actions of the mind is obtained by controlling the breath.
Since Kriya Yoga is based on breath, you can practice this special technique during the whole day and in whatever activity you do. When it comes to sitting for meditation, it may be practiced whenever you have time.
Source : © Swami Shankarananda Giri, Kriya Yoga Ashram, Bhubaneswar, Orissa, India, All rights reserved