Verse 8.8.3

तौ होचतुर्यथैवेदमावां भगवः साध्वलंकृतौ सुवसनौ परिष्कृतौ स्व एवमेवेमौ भगवः साध्वलंकृतौ सुवसनौ परिष्कृतावित्येष आत्मेति होवाचैतदमृतमभयमेतद्ब्रह्मेति तौ ह शान्तहृदयौ प्रवव्रजतुः ॥ ८.८.३ ॥

tau hocaturyathaivedamāvāṃ bhagavaḥ sādhvalaṃkṛtau suvasanau pariṣkṛtau sva evamevemau bhagavaḥ sādhvalaṃkṛtau suvasanau pariṣkṛtāvityeṣa ātmeti hovācaitadamṛtamabhayametadbrahmeti tau ha śāntahṛdayau pravavrajatuḥ || 8.8.3 ||

3. The two of them said, ‘Revered sir, just as we are well-dressed in fine clothes, and neat and clean, in the same way, these two reflections are well-dressed in fine clothes, and neat and clean.’ Prajāpati said: ‘That is the Self. It is immortal and fearless. It is Brahman.’ The two of them left then, happy in mind.

Word-for-word explanation:

Tau ha ucatuḥ, they both said; bhagavaḥ, sir; yathā eva, just as; idam āvām, we two here; sādhu-alaṅkṛtau, well-dressed; suvasanau, wearing fine clothes; pariṣkṛtau svaḥ, are neat and clean; evam eva, like this; bhagavaḥ, lord; imau, these two [reflections]; sādhu-alaṅkṛtau, well-dressed; suvasanau, wearing fine clothes; pariṣkṛtau iti, neat and clean; iti ha uvāca, [Prajāpati] said; eṣaḥ ātmā, this is the Self; etat amṛtam, this is immortal; abhayam, fearless; etat brahma iti, this is Brahman; tau, both of them; śāntahṛdayau pravavrajatuḥ, left happy in mind.

Commentary:

Now Indra and Virocana see themselves with fine clothes and ornaments on. Just as it should have been obvious to them that the Self is not the body with its hair and nails, even more so it should be obvious that the Self is not the body with its fine clothes, as they were not wearing those clothes before. Prajāpati was trying to provoke them into thinking. Is the body with its fine clothes deathless and free from fear? If it is unchanging, why does it look different when you put on different clothes? But they went away very happy, thinking they had the answer.

Ordinarily our minds are wavering back and forth with doubts and indecision. That is the nature of the mind. But the Upaniṣad says Indra and Virocana went away śāntahṛdaya, with their minds at rest. That means without any doubt, without any question. It means they think they have received a satisfactory answer to their question, and the problem is solved.