Bhashya
पूर्ववदेतं त्वेव त इत्यादिमुक्त्वा तद्यत्रैतत्सुप्त इत्यादि व्या-ख्यातं वाक्यम् ।अक्षिणि यो द्रष्टा स्वप्ने च महीयमानश्च-रति स एषः सुप्तः समस्तः संप्रसन्नः स्वप्नं न विजानाति,एष आत्मेति ह उवाच एतदमृतमभयमेतद्ब्रह्मेति स्वाभिप्रे-तमेव ।मघवान् तत्रापि दोषं ददर्श ।कथम् ? नाह नैवसुषुप्तस्थोऽप्यात्मा खल्वयं संप्रति सम्यगिदानीं च आत्मानंजानाति नैवं जानाति ।कथम् ? अयमहमस्मीति नो एवे-मानि भूतानि चेति ।यथा जाग्रति स्वप्ने वा ।अतोविनाशमेव विनाशमिवेति पूर्ववद्द्रष्टव्यम् ।अपीतः अपि-गतो भवति, विनष्ट इव भवतीत्यभिप्रायः ।ज्ञाने हि सतिज्ञातुः सद्भावोऽवगम्यते, न असति ज्ञाने ।न च सुषुप्तस्यज्ञानं दृश्यते; अतो विनष्ट इवेत्यभिप्रायः ।न तु विनाशमेवआत्मनो मन्यते अमृताभयवचनस्य प्रामाण्यमिच्छन् ॥
In plain words
As in the previous sections, when the text says, 'But indeed, I will explain this further to you,' it refers to the sentence beginning with 'where this one is asleep,' which has already been explained. The conscious seer who operates in the eye during waking, and who experiences glory in dreams, is the very same one who, in deep sleep, is fully withdrawn, serene, and free from dreams. Prajāpati declared: 'This is the Self; this is the immortal, the fearless, this is Brahman.' This was indeed his intended teaching. Yet Indra found a flaw even here. How? He realized that the self in deep sleep does not have clear self-awareness at that moment; it does not know 'I am this,' nor does it recognize other beings, as it does when awake or dreaming. Therefore, the phrase 'gone to destruction' must be understood as 'as if destroyed,' just as before. 'Gone into' means merged; the meaning is that it appears as if annihilated. We only know a knower exists when there is active knowing; when there is no knowing, we cannot perceive the knower. Since no active knowing is seen in a sleeping person, it seems as if he is destroyed. Yet Indra does not believe the Self is actually annihilated, for he wishes to uphold the truth of Prajāpati's words that the Self is immortal and fearless.
Close to the Sanskrit
As before, having spoken 'But indeed this to you' etc., that sentence beginning with 'where this one is asleep' is explained. The seer who is in the eye, and who moves being magnified in dream, that same is asleep, withdrawn, serene, does not know dream; 'this is the Self,' indeed he said, 'this is the immortal, the fearless, this is Brahman'—this is precisely his own intended meaning. Indra saw a defect there too. How? 'Indeed, this self, even though situated in deep sleep, does not now properly and at this moment know itself; it does not know thus.' How? '"This I am" nor indeed these beings.' Just as in the waking state or in dream. Therefore, 'only destruction' should be understood as 'as if destruction', as before. 'Gone into' means 'entered into'; 'becomes as if destroyed' is the meaning. For when knowledge is present, the existence of the knower is understood, not when knowledge is absent. And the knowledge of the sleeping person is not seen; therefore, 'as if destroyed' is the meaning. But he does not think actual destruction of the Self, wishing to maintain the authority of the statement about immortality and fearlessness.