Verse 6.13.1-2

लवणमेतदुदकेऽवधायाथ मा प्रातरुपसीदथा इति स ह तथा चकार तं होवाच यद्दोषा लवणमुदकेऽवाधा अङ्ग तदाहरेति तद्धावमृश्य न विवेद ॥ ६.१३.१ ॥
यथा विलीनमेवाङ्गास्यान्तादाचामेति कथमिति लवणमिति मध्यादाचामेति कथमिति लवणमित्यन्तादाचामेति कथमिति लवणमित्यभिप्रास्यैतदथ मोपसीदथा इति तद्ध तथा चकार तच्छश्वत्संवर्तते तं होवाचात्र वाव किल तत्सोम्य न निभालयसेऽत्रैव किलेति ॥ ६.१३.२ ॥

lavaṇametadudake'vadhāyātha mā prātarupasīdathā iti sa ha tathā cakāra taṃ hovāca yaddoṣā lavaṇamudake'vādhā aṅga tadāhareti taddhāvamṛśya na viveda || 6.13.1 ||
yathā vilīnamevāṅgāsyāntādācāmeti kathamiti lavaṇamiti madhyādācāmeti kathamiti lavaṇamityantādācāmeti kathamiti lavaṇamityabhiprāsyaitadatha mopasīdathā iti taddha tathā cakāra tacchaśvatsaṃvartate taṃ hovācātra vāva kila tatsomya na nibhālayase'traiva kileti || 6.13.2 ||

1-2. [Uddālaka said,] ‘Put this lump of salt into water and come to me in the morning.’ Śvetaketu did as he was told. Uddālaka said to him, ‘My son, bring me the salt that you put in the water.’ Śvetaketu looked, but he could not find it, as the salt had dissolved in the water. [Uddālaka said,] ‘My son, drink the water at the surface.’ [Śvetaketu did that, and Uddālaka asked,] ‘How does it taste?’ [Śvetaketu replied,] ‘It is saline.’ [Uddālaka then said:] ‘Drink it from the middle. How does it taste?’ ‘It is saline.’ ‘Drink it from the bottom. How does it taste?’ ‘It is saline.’ ‘Throw the water away and then come to me.’ Śvetaketu did so. The father said to him:

Word-for-word explanation:

Lavaṇam etat, this salt; udake, in water; avadhāya, put; atha mā, then to me; prātaḥ, in the morning; upasīdathāḥ iti, come; saḥ, he [Śvetaketu]; tathā, that way; ha cakāra, did; tam ha uvāca, he said to him [to Śvetaketu]; yat lavaṇam, that salt which; doṣā, at night; udake avādhāḥ, you put into water; aṅga, my son; tat, that; āhara iti, bring it back; tat, that; ha avamṛśya, having searched for; na viveda, he did not find, Yathā, since; vilīnam eva, it had disappeared [in the water]; aṅga, my son; asya antāt ācāma iti, drink from its surface; katham iti, how is it; lavaṇam iti, saline; madhyāt ācāma iti, drink from the middle; katham iti, how is it; lavaṇam iti, saline; antāt ācāma iti, drink from the bottom; katham iti, how is it; lavaṇam iti, saline; abhiprāya etat, throw this away; atha mā upasīdathāḥ iti, then come to me; tat ha tathā cakāra, he did likewise; tat, that [salinity]; śaśvat, always; saṃvartate, prevails everywhere; tam ha uvāca, he said to him [to Śvetaketu]; atra vāva kila, here [in this body]; somya, O Somya; sat, the self [exists]; na nibhālayase, [but] you do not see it; atra eva kila iti, here [in the body].

Commentary:

‘There is salt in every part of the water, yet you cannot see it. Similarly, O Somya, Sat [the Self] is here in this body, yet you cannot see it in the body.’

The question that is being examined is, why are we not able to perceive the Self, which is the essence of our being? It is because the Self is all-pervasive. The Self and I are one and the same. If the Self were something separate from me, then I could see it. Can I see myself? I can see myself if I have a mirror—something else. But there is nothing but the Self, so how can I see it? It’s not possible.

Because you don’t see something that doesn’t mean it does not exist. The process of seeing involves separate entities: the seer and the seen—that is, the subject and the object. These two must be separate. Then only the process of seeing can take place. But if there is only one, who sees whom?

The Upaniṣad gives two examples of how things may exist that we do not perceive. One is of the banyan tree and the seed, and the other is of salt in water. Suppose you put a lump of salt in a glass of water. Soon the salt dissolves. You no longer see it, but that doesn’t mean it is not there. If you taste the water you will find that it tastes salty throughout.

Similarly, just because we do not see the Self, that doesn’t prove it does not exist. Reality is not something that is perceptible to our sense organs. It is vākyamanātīta—beyond speech and mind, beyond thought. Words fail to describe it and our mind cannot grasp it, because it is so fine, so subtle. The Self is not something on the relative plane that we can see or touch. Our sense organs are very limited. Our eyes can see things only up to a point and beyond that they cannot see any more. There are many things around us that our eyes cannot see. Similarly with our hearing and other organs. So, in order to perceive the Self we must go beyond the relative plane to the transcendental level.

Śaṅkara says that this body is a product of food (or, earth), water, and fire, and the Self is within this body. Though you cannot see the Self, it permeates the body—just as the salt permeates the water