This is a minor Upaniṣad of just 22 verses belonging to the Kṛṣṇa Yajurveda.
It starts with an oft-quoted statement that it is the mind that is responsible for either bondage or liberation. When attached to sense objects it leads to bondage; when freed from the same, it leads to liberation. Hence it should be freed from the bondage of sense-life.
It then delineates the process of meditation by which the mind bereft of sense-attachments is fixed in the region of the heart on Brahman. Meditation on Brahman can be practised first through the sound of Om, and then directly.
This is followed by an exposition of Brahman-ātman with the usual adjectives like niṣkalam (partless), nirañjanam (stainless), aprameyam (immeasurable) and so on. Then the Upaniṣad describes how Brahman, the one without a second, appears as many, with the simile of moon and its reflections in water, and, the sky and pots.
It puts forth the theory of two kinds of knowledge, of Śabda-Brahman and Para-Brahman.
The former is the Vedas and their branches. A mastering of these can help in leading to the latter, which has to be realized through contemplation. This contemplation is likened to the process of churning milk to get butter, or churning the pieces of araṇi (See ARAṆI.) to get fire. The Upaniṣad ends with a statement of the jñānī, a man of realization, reflecting on his realization of his identity with Brahman.
It is interesting to note that there is another Upaniṣad called Brahmabindu Upaniṣad which is almost identical with this Upaniṣad.
See also UPANIṢADS.