The Bṛhadāraṇyaka Upaniṣad which forms an important part of the Śatapatha Brāhmaṇa of the Śukla Yajurveda is by far the biggest of the extant Upaniṣads. The Śatapatha Brāhmaṇa is found to be in two śākhās or recensions, the Kāṇva and the Mādhyandina. Hence the Upaniṣad also is found to have two recensions.
The seventh section—each such section is known as a ‘brāhmaṇa’—of the third chapter of this Upaniṣad is called Antaryāmi Brāhmaṇa since it deals with the topic of Brahman as the antaryāmin (‘the indwelling spirit’).
The third chapter starts with the convening of a conference of ‘knowers of Brahman’ by the king Janaka of Videha, who expresses a desire to know the best among them (brahmiṣṭha), and offers rich presents. The sage Yājñavalkya comes forward to take away the presents even before proving his mettle in the assembly. This naturally enrages the assembled sages who start challenging him with intricate philosophical queries. However, Yājñavalkya proves more than a match for all of them.
The seventh brāhmaṇa—which is the Antaryāmi Brāhmaṇa—starts with the question of Uddālaka Āruṇi about the antaryāmin or the indwelling spirit in the universe. Yājñavalkya replies that it is the Ātman or the Self that resides in everything, whether it is the elements like the earth, or the worlds like heaven or living beings or sense organs or mind, and controls them all from within. He knows them but they know him not. He is actually the knower and can never become an object of perception or knowledge. He is the eternal Self of all.
If the Kāṇvaśākhā stops with this, the Mādhyandinaśakhā continues the description and adds ‘ya ātmani tiṣṭhan...’ (‘who, remaining inside the ātman...’) which lends strength to the belief that the ātman (the individual self) and Brahman (the Supreme Self) are different and that the latter controls the former. This comes in handy for the dualistic schools like Viśiṣṭādvaita Vedānta to defend their position.