Verse 6.1.3

श्वेतकेतो यन्नु सोम्येदं महामना अनूचानमानी स्तब्धोऽस्युत तमादेशमप्राक्ष्यः येनाश्रुतं श्रुतं भवत्यमतं मतमविज्ञातं विज्ञातमिति कथं नु भगवः स आदेशो भवतीति ॥ ६.१.३ ॥

śvetaketo yannu somyedaṃ mahāmanā anūcānamānī stabdho'syuta tamādeśamaprākṣyaḥ yenāśrutaṃ śrutaṃ bhavatyamataṃ matamavijñātaṃ vijñātamiti kathaṃ nu bhagavaḥ sa ādeśo bhavatīti || 6.1.3 ||

3.‘—that teaching by which what is never heard becomes heard, what is never thought of becomes thought of, what is never known becomes known?’ [Śvetaketu asked,] ‘Sir, what is that teaching?’.

Word-for-word explanation:

Yena, [that teaching] by which; aśrutam, what is never heard; śrutam bhavati, becomes heard; amatam matam, what is never thought of [becomes] thought of; avijñātam vijñātam iti, what is never known [becomes] known; bhagavaḥ, O lord; katham nu saḥ ādeśaḥ bhavati iti, what is that teaching?

Commentary:

How can there be such a thing by knowing which you know everything else? This is what is puzzling Śvetaketu. Is it possible that by knowing one thing you also know something else? Separate things are to be known separately. But the claim is being made here that unless you know the Self you know nothing. And if you know the Self you know everything. This sounds like an absurd proposition.

This ādeśa, or teaching, that Āruṇi is talking about is the secret that opens up one’s eyes, that makes one conscious of the fact that until and unless one knows the Self, one knows nothing.