They focused their attention on the ultimate power behind the sacrifices, the force that gives light to all the natural phenomena of the world. To look beyond the natural, the scholars used meditation centered on the inner self. Life began to be viewed as a cycle of birth and rebirth where the present life depended on the actions of the former. But this cycle could be escaped if one were to gain the correct truth by shifting ones attention from the external world to find the inner truth. By finding the difference between the real and unreal, the sage comes to find that within everyone is an unchanging, eternal essence known as the "self." The Upanishads identify this self with the supremely ultimate; the mysterious entity of the universe that is hidden from ordinary perceptions. This ultimate is said to be beyond comprehension, and is known as "Brahman.".
According to the Upanishads, the ordinary perceptions of natural beings are guided by ignorance. In order to receive true enlightenment one must gain control over ones thoughts and body through a gradual disciplined process called yoga. In yoga, one learns to switch their attention from the outwardly natural senses and to direct their energy inward opening their perceptions to the inner self. Brahmas is said to be the sole reality, while the perceived world is a misguided realty.
A similar system that shares many of the initial traits is outlined in the Yoga Aphorisms of Patanjali. Differing from the Upanishadic outline of a monistic system where Brahmas is the sole reality, Pantajali's yoga system sees reality in two parts - matter and spirit. The main goal of this system is the separation of the spirit from matter, where the main goal of the Upanishad's is the realization of the self and Brahmas. .
The practice of mind control precedes the teachings presented in the Upanishads. Both the Upanishads and Patanjali's yoga system caused a shift in thought from the sacrifices to the gods in early Vedic period to the path of liberation that is accepted through yoga.