Verse 2.2.9

हिरण्मये परे कोशे विरजं ब्रह्म निष्कलम् ।
तच्छुभ्रं ज्योतिषं ज्योतिस्तद्यदात्मविदो विदुः ॥ ९ ॥

hiraṇmaye pare kośe virajaṃ brahma niṣkalam |
tacchubhraṃ jyotiṣaṃ jyotistadyadātmavido viduḥ || 9 ||

9. The stainless indivisible Brahman, the pure, the light of all lights is in the innermost sheath of golden hue. That is what the knowers of the Atman know.

Shankara’s Commentary:

Com.—The three following texts briefly elucidate the meaning already expressed. Hiranmaye, golden, i.e., full of light, or bright with intelligence and knowledge. ‘The highest sheath’, sheath, as it were, of a sword; highest, because it is the place where “the Atman is realised as located” and because it is the innermost of all. Virajam, free from the taint of ignorance and all other faults. Brahma, because it is the greatest of all and Atman of all. Nishkalam, that from which the kalas had proceeded, i.e., devoid of parts; because it is untainted and devoid of parts, therefore it is subhram or pure. The light of all lights, whose light enlightens even those that illumine all other things such as fire, etc. The meaning is that the brightness of even the fire, etc., is due to the splendour of the intelligence of the Brahman within; the light of the Atman is the highest light which is not illumined by other lights. ‘The knowers of the atman’, those discerning men who know the Self as the witness of the objective states of consciousness regarding sound and the rest; as it is the highest light, it is only those who follow (are in) the subjective state of consciousness, not others, who follow (are in) the perceptions of external objects, that know it.