ऋतं पिबन्तौ सुकृतस्य लोके गुहां प्रविष्टौ परमे परार्धे ।
छायातपौ ब्रह्मविदो वदन्ति पञ्चाग्नयो ये च त्रिणाचिकेताः ॥ १ ॥

ṛtaṃ pibantau sukṛtasya loke guhāṃ praviṣṭau parame parārdhe |
chāyātapau brahmavido vadanti pañcāgnayo ye ca triṇāciketāḥ || 1 ||

1. The two, who enjoy the fruits of their good deeds, being lodged in the cavity of the seat of the supreme, the knowers of Brahman call shadow and light, as also those who maintain five fires and have thrice propitiated the Nachiketa fire.

Shankara’s Commentary:

The connection of the present valli is this. Knowledge and ignorance have already been described, as leading to many contrary results; but each of them has not been described, in its own nature, with its results. The imagining of the analogy of the chariot is for the purpose of determining them, as also for the easy understanding of the subject. Thus two atmans are here described for the purpose of distinguishing between the attainer and the attained and the goer and the goal. Drinking, i.e., enjoying; truth, i.e., the fruits of the enjoyer, on the analogy of using the expression ‘the umbrella-carriers go’ when not all of them carry umbrellas. Sukritasya means of deeds done by themselves and is connected with the previous word ‘fruits.’ Loke, means in this body. Guham pravishtau, means lodged in intelligence. Parame, superior in relation to the space of the akas of the external body. Parardhe, in the abode of Brahman, for, there, can Brahman be realised. The meaning is that they are lodged in the akas within the cavity of the heart; again they are dissimilar like shadow and light, being within the pale of Samsara and free from Samsara, respectively. So do the knowers of Brahman tell; not those alone who do not perform Karma say so; but also householders maintaining five sacrificial fires, and others by whom the sacrificial Nachiketa fire has been thrice lit.