Verse 6.9.4

स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा तत्त्वमसि श्वेतकेतो इति भूय एव मा भगवान्विज्ञापयत्विति तथा सोम्येति होवाच ॥ ६.९.४ ॥
॥ इति नवमः खण्डः ॥

sa ya eṣo'ṇimaitadātmyamidaṃ sarvaṃ tatsatyaṃ sa ātmā tattvamasi śvetaketo iti bhūya eva mā bhagavānvijñāpayatviti tathā somyeti hovāca || 6.9.4 ||
|| iti navamaḥ khaṇḍaḥ ||

4. ‘That which is the subtlest of all is the Self of all this. It is the Truth. It is the Self. That thou art, O Śvetaketu.’ [Śvetaketu then said,] ‘Sir, please explain this to me again.’ ‘Yes, Somya, I will explain it again,’ replied his father.

Word-for-word explanation:

Saḥ yaḥ, that which; eṣaḥ, this; aṇimā, the subtlest of all; idam sarvam aitadātmyam, the Self of all this; tat satyam, that is the Truth; saḥ ātmā, that is the Self; tat, that; tvam, you; asi, are; śvetaketo iti, O Śvetaketu; bhagavān, sir; bhūyaḥ eva, again; mā, to me; vijñāpayatu iti, will you please explain; tathā, so be it; somya iti, O Somya; ha uvāca, he [the father] said. Iti navamaḥ khaṇḍaḥ, here ends the ninth section.

Commentary:

“Tat tvam asi”—thou art that. This is called the mahāvākya, the great saying, it is the magic formula. If your mind has been purified, as soon as the mahāvākya is uttered your eyes are opened and you realize your own Self. But this can happen only after a long process of preparation. It does not come by a fluke. After years of hard work and after shedding many tears, at last one day your mind becomes pure and free from ego. You have attained cittaśuddhi, purification of the mind. Your mind is then like a clean mirror. Now there is a layer of dust on the

Once you know who you are you can never be deluded. Can there be darkness where there is light? If you are really enlightened there can be no room for ignorance in your mind. But without cittaśuddhi, even if the teacher tells you that you are the Self, you will not believe it. You will think: ‘No, that is nonsense. I am this body.’ The father is again telling Śvetaketu, ‘You are That,’ but still it is not clear to him.

How does it become clear? First we must study the Upaniṣads. Then we have to try and grasp the ideas intellectually. So long as the teacher is giving us instructions the idea fascinates us. That’s fine, but it’s not enough. We must realize it. We must feel it in the very depth of our being.

Spiritual knowledge does not come through an intellectual process. It’s something more, something deeper, something that touches the very root of our being. It’s an experience. When you have this experience you are totally transformed. You are not the same individual anymore.