Ancient India had many sects of asceticism and renunciation, including Sramanas, Parivrajakas, Ajivkas, Lokayatas, Vratyas, Samkhyas, Bhaktas, Bhagavatas, and Pasupatas. In pursuit of deliverance they renounced earthly life. Some were as ancient as, or even older than, the Vedic faith. The Sramanas and Parivrajakas were low caste mendicants who, as part of their vows, subjected themselves to the difficulties of life, renounced worldly life, moved from village to village, pursued alms and practiced austerities.In the earlier days the Vedic people had hated them for their practices and worship methods. This did not, however, stop the Sramanas from pursuing their practices and persisting in their methods. The methods seem to find acceptance even among Vedic people at some point.
The introduction of ascetic practices into the Vedic tradition has most certainly contributed to the advent of yoga as a special branch of wisdom and an important spiritual discipline in Hinduism. Prior to this development, the Vedic religion had the tradition of hermits and forest dwellers (vanaprasthas), who lived in hermitages in seclusion and studied the mystical aspects of Vedas and advanced ritual knowledge. They were probably responsible for the early development of Upanishadic thought focused mainly on Brahmana rituals and ritual-based philosophy, such as the one found in the Chandogya and Brihadaranyaka Upanishads.
Yoga's introduction into Vedic culture had been incremental and fragmentary. It started vaguely with the notion that the rituals (karmakanda) constituted inferior knowledge or even ignorance (vidya) as compared to Self or Brahman's true knowledge (vidya), which led to liberation. Rituals were important for world order and regularity, peace and prosperity, but would lead only to karma and rebirth. Since rituals are often performed for earthly ends, they will not free the beings from the process of life and death. Liberation can only be accomplished by understanding the Self or the Brahman. The claim strongly favored a significant change from ceremonial knowledge to spiritual knowledge in emphasis.
We can clearly see the change in the Mundaka Upanishad, as it poses the statement that sacrifices are inferior, and the boats of those who perform them are unstable. If freedom is the aim then rituals should be avoided. The deluded may rejoice in them, but they would only incur negative consequences and repeatedly return to take on another birth from the ancestral world. In comparison, those who lead austere lives in the forests and practice tapas with faith and calm minds, renounce the world and cast off their desires, go through the door of the sun to Brahman 's realm and never come back.
Another major change was the discovery that breath was superior to all the organs in the body, including the mind, and it was possible to control both the mind and the body by regulating breath. The yoga techniques both of pranayama and of pratyahara work on the same principle. The Upanishads clearly acknowledge breath superiority. Breath is the corporeal lord. It is the cleanser that keeps the evil at bay. It is similar in essence and in function to the Self. The body is alive for as long as oxygen sustains it.And all the organs are able to conduct their functions and stay in their respective spheres because of oxygen. Thus it is possible to control the mind, the body and the senses by regulating breath in the body. Ideas like these may be responsible for the yoga's heavy focus on pranayama practice before meditation and concentration starts.
The early Upanishads also accept the distinction between the body and self. The body is perishable, the Self being indestructible. The Self is the transcendental truth, beyond mental and senses. Thus, vision, birth, or awareness can not be understood, but only by suppressing both the mind and the senses and eliminating the impurities that obstruct their clear view. If the mind is absolutely quiet and the senses sleep fully as if they are non-existent, the Self will show itself as a mirror whose surface is washed.Since this condition is not ordinarily attainable, the Upanishads clearly acknowledge the need for a spiritual discipline to prepare mind and body to attain the transcendental truth.
Several Upanishads have references to yoga and Yoga techniques. Some Shaiva and Vaishnava Upanishads that are devoted exclusively to the yoga theory and practice are known as Upanishads of Yoga. Nevertheless, as they are works of later day, compiled probably from pre-existing works, they are not of great value from a historical perspective, except for comparative analysis and technical information. References to yoga are found among the earliest Upanishads in the Katha, Svetasvatara, and Maitri Upanishads. Through them we can discern a progressive development of the yoga methods and practices.
The Katha Upanishad declares Yoga to be the state of mental stability that the restraint of the senses makes possible. It is the state in which the mind is stable and there is firm restraint on the senses. The Self should be understood as both a reality of existence and an eternal reality. One comes to that realization and becomes immortal only when all desires are cast away in the heart, and all the bonds are cut off. The Self then reveals itself to be sitting in the heart, having the size of a thumb.
The Upanishad Svetasvatara contains more specific information about yoga techniques, and the results that can be achieved by their practice. This explains how one should practice meditation by keeping the three sections of the upper body upright and removing the mind and the senses into the heart to cross the ocean of births and death and fear of death by Brahman 's boat itself. Holding the air in his body, restricting his movements to the bare minimum, he would breathe through his nostrils, reducing the wind, regulating his mind with utmost caution, the way wild horses are yoked to a chariot.
The Upanishad also suggests the conditions under which yoga can be practiced and what perfections its regular practice may bring about. In order to practice yoga, one should choose an ideal location, simple and clear, free of pebbles, fire and gravel, in a hidden cave, safe from wind disruptions, with calming sounds of flowing water coming from nearby, and features pleasing to the mind and eyes. With the activity when the mental and body alteration is reversed, one is free from illness, aging , and death. He experiences lightness, good fitness, steadiness, skin color change, voice smoothness, a nice body odor and mild excretions.Just as the mirror covered with dust shines brightly after being cleansed, so does the person whose mind and body are cleansed of impurities, and who sees the Self within himself.
So we can see that the Upanishads were familiar with the principles and practice of yoga, and shared with the philosophy of yoga many common beliefs and ideas. In them we can discern a gradual structure of yoga techniques and their more formal nature, as tradition has recognized the importance of spiritual and ascetic practices and internal rituals in order to attain liberation from death and rebirth. For the Upanishads, liberation through knowing Atman and Brahman is the highest priority for which yoga is one of the means for purifying mind and body and suppressing Nature's modifications.
Other forms of Yoga like Karmayoga, Jnanayoga, Bhakti yoga, and Sanyasa yoga are also recognized by the Upanishads. We also recognize both Brahman and Atman, as opposed to Yoga which recognizes only the individual self. Thus, while the Upanishads share with Yoga many common beliefs, they retain their distinction and a broader philosophical and spiritual vision.