Upaniṣad means “sitting near,” alluding to the tutorials given by a guru to his disciples (who would traditionally sit “at his feet’). The Upaniṣads are philosophical texts delineating some of the key concepts within Hinduism, including notions of the soul, reincarnation, karma, Brahman and liberation. The Upaniṣads are sometimes considered the beginning of direct spiritual instruction within the Vedas. The traditional number of Upaniṣads is 108, though there are many more, especially of recent origin. Of these, 13 are usually considered most important.
Vedanta Sutras
The Vedanta Sutras (also called the Brahma Sutras) are an attempt by the sage Vyasa (Badarayana) to systematise the teachings of the Upanishads. There are a total of 550 aphorisms divided between four chapters. Various authors wrote lengthy commentaries upon them, giving rise to the many different and often conflicting schools of Vedanta (see Vedanta and Mimaṁsa). Important commentaries – considered smṛti – include the Śariraka Bhaṣya by Śankara, the Śri Bhaṣya by Ramanuja, the Śrikara Bhaṣya by Śripati, and the Govinda Bhaṣya by Baladeva.
Because people are less philosophically inclined in Kali-Yuga, the Upaniṣads and Vedanta Sutra are considered difficult to understand without the guidance of the supplementary smriti literature.
Scriptural Passages
“Do not stay in illusion, go to the eternal reality. Do not remain in darkness, approach the light. Do not remain in this place of death – become immortal!”
Brihad-Aranyaka Upaniṣad 1.3.28
“The Personality of Godhead is perfect and complete, and because He is completely perfect, all emanations from Him, such as this phenomenal world, are perfectly equipped as complete wholes. Whatever is produced of the Complete Whole is also complete in itself. Because He is the Complete whole, even though so many complete units emanate from Him, He remains the complete balance.”
Śri Iśopaniṣad Invocation Mantra