Verse 2.80

Sanskrit text and transliteration:

गुहायां निहितं यस्मादेतस्मादात्मनस्तथा ।
ब्रह्मात्मशब्दयोस्तस्मादैकार्थ्यमवसीयते ॥ ८० ॥

guhāyāṃ nihitaṃ yasmādetasmādātmanastathā |
brahmātmaśabdayostasmādaikārthyamavasīyate || 80 ||

English translation of verse 2.80:

Inasmuch as Brahman is spoken of as what is laid in the cave, and since from (Brahman), this Self, (ether, etc., are said to have come), the identity of meaning of the two words “Brahman” and “Ātman” is, therefore, ascertained.

Notes:

It may be argued that Brahman is not infinite since it is limited by the Self which is different from it. But this argument is wrong since the Self is non-differcnt from Brahman. It is significant that the Upaniṣad uses the term "Brahman" in the place where the term “Ātman” is normally used, and vice versa. Whereas we would usually say that the Self is seated in the intellect (buddhi) which is here referred to as the “cave”, and that it is the witness of all mental modes (sarvabuddhivṛtti-sākṣī), the Upaniṣad in the sequel refers to Brahman as existing in the intellect and as its witness. It only means that Brahman is no other than the Self of the individual. Again, while Brahman is usually referred to as the source of ether, etc., the Upaniṣad in the sequel points out that from that Brahman (tasmāt), i.e., from this Self (etasmāt ātmanaḥ), ether came into existence. This again confirms the non-difference between Brahman and Ātman. If so, the contention that the Self, being different from Brahman, limits it is untenable.

The two passages referred to in the verse are: (1) yo veda nihitaṃ guhāyām parame vyoman and (2) tasmādvā etasmādātmana ākāśaḥ sambhūtaḥ.