So, it is not possible to perceive Reality; it can only be inferred. And the inference can be so convincing, so firm in its being established as a final solution to the problem of diversity, that the mind can contemplate upon it. The philosophical inference is not a real perception. It is an activity of the mind alone. No doubt it is an activity of the higher mind, but it is not a realisation; it is not an experience. However it can be so mathematically precise, so scientifically perfect, that it can drive conviction into the mind, and where conviction is complete, the mind can go nowhere else. It can go to that alone. It is lack of conviction that makes us drift from one thing to another. But when the conviction is complete and it is founded well in one's own heart, in one's own feelings, then meditation follows automatically. 'If this cannot be achieved, one clings only to diversity; the achieved state is then of birth and death.' Mṛtyoḥ sa mṛtyum ᾱpnoti ya iha nᾱneva paśyati: No one can escape birth and death; no one can be free from transmigratory metempsychosis as long as there is belief in the diversity of objects, because the conviction and the belief that there are really multitudinous objects in the world compels one to run after them. It is impossible for one to be free from one's longing for things which are seen with the eyes as real, because they are believed to be such on account of the incapacity of the lower mind to infer the existence of something which is underlying them. The conviction that diversity is true, ultimately, compels the mind to long for finitude. One takes finite objects as targets of experience and satisfaction. Finite things cannot satisfy the mind, because a finite object is hanging for its existence on certain other finite objects. There is an interconnectedness of things, but this is imperceptible to the senses. Relying on the truth of sensory perception, there is no satisfaction; the body is shed in a condition of mental dissatisfaction, and this unsatisfied condition of the mind during which the body is shed becomes the cause of rebirth for the satisfaction of unfulfilled desires. So it is the perception of diversity that leads to rebirth. The senses, therefore, are not the real guides of an individual in the comprehension of Reality. It is the higher mind, the higher reason alone, that should be taken here as our mentor.

20. ekadhaivᾱnudraṣtavyam etad aprameyaṁ dhruvam, virajaḥ para ᾱkᾱśᾱd aja ᾱtmᾱ mahᾱn dhruvaḥ.

Ekadhaivᾱnudraṣtavyam: The perception of Reality should be practised in our daily activity. It is not easy to do it because the senses are our friends, and not so the higher mind. Unfortunately, we never take the higher mind to be our friend in our daily activities. It rarely functions. Even if it tries to peep through, the activities of the senses overwhelm it. Like a mighty wave that dashes down all things that come before it, the sense activity puts down or stifles the activity of the higher mind, on account of the vehemence of attachment to things. But 'practice makes perfect'; so the adage goes. A daily attempt has to be put forth by everyone to see that the senses do not gain an upper hand, and that you do not trust the report of the senses too much because, as we have seen, they are bad friends. They are going to bind us one day or the other and throw us to hell. The higher mind has to be taken as our real guide and philosopher. The oneness of being is, therefore, to be practised as a regular routine in spite of the overwhelming vehemence of sense activity. It is like taking a bath in the tumultuous ocean, which is not particularly easy due to the waves that are constantly trying to press you into the bosom of the ocean. Likewise, the senses will not allow you to contemplate unity. Who can see unity? You open the eyes and see many things, many objects. The eyes are not the guides; the ears are not the guides; no particular sense-organ can be regarded as an instructor to us in the perception of Truth. In spite of the multitudinousness of variety that the senses present before us, a very piercing intelligence has to work behind them and 'the practice of the perception of the unity inferred in the background of this sensory diversity should be made a regular programme of daily life' - ekadhaivᾱnudraṣtavyam.

Etad aprameyaṁ dhruvam, virajaḥ: It is eternal Reality, no doubt, but it is 'immeasurable' to the senses. However much you may strain your eyes, you cannot see it. Whatever be the instrument of observation that you use, it cannot be observed, because the subtlety of physical instruments is nowhere comparable to the subtlety of this Supreme object of quest of this goal of one's life. There is no instrument conceivable other than the mind. It is our superior mind only that is going to help us in convincing us of the nature of Truth. Any kind of activity, speaking or hearing, seeing or touching, tasting or smelling, whatever it be, is not the correct philosophical instructor for a seeker of Truth. The real instructor is the higher philosophical and logical reason which alone can tell us that there is an apprehension of a Being which is more profound than the finite objects which are presented by the senses. Though immeasurable to the senses, it is measurable by the higher intellect. 'It is free from the Rajas, or the character of distraction, which preponderates in the senses' - virajaḥ.

Para ᾱkᾱśᾱd aja ᾱtmᾱ: 'It is superior even to the extensiveness of space', and therefore we find it difficult to conceive even with the mind. The infinitude of the Supreme Being is inconceivable because it is far more infinite than even the conceptual infinite of spatiality that we think of in our minds. It is more difficult to conceive this unity for another reason also. It is the Self of all beings - Ātman as well. First of all, the difficulty is due to the incapacity of the senses to apprehend its being. It cannot be seen. However much you may scratch your head, it is not there. By chance, if you do stumble upon it through the work of pure inductive reason, it is still difficult to make it a part of the daily meditation, because is not merely an infinitude of objectivity, but is the Self, also. It is hard for one to combine these two aspects; it is almost like a circus feat, a kind of acrobatics that you have to perform through the high reason. How is it possible to conceive, first of all, an endlessness of existence? And if it is practicable at all, it becomes even more difficult when it is identified with the Selfhood of beings. An endlessness of Being identified with the Selfhood of beings is hard to conceive. But that is the key to true meditation. 'This is the great Being, the eternal' - para ᾱkᾱśᾱd aja ᾱtmᾱ mahᾱn dhruvaḥ.

21. tam eva dhīro vijñᾱya prajñᾱṁ kurvīta brᾱmaṇaḥ nᾱnudhyᾱyᾱd bahῡn śabdᾱn, vᾱco viglᾱpanaṁ hi tat iti.

Here, like a mother, the scripture gives a piece of good advice. 'One should not read too much or speak too much. It is a waste of energy.' Though a little of study and education is necessary in the earlier stages, too much of bookishness is not going to help in the end, and not too much speech, also. One has to restrain the tongue, because through it energy is spent too much. Speaking too much, reading too much are not advantageous in the higher stages of spiritual practice. 'A heroic seeker, a bold aspirant, should take this alone as the goal of life, and should not divert his attention to objects which are finite in their nature.' Having understood the character of this Reality through the analytical reason, one should try to fix one's mind in this understanding. Practice should follow correct understanding. One should not be too eager to practice without proper understanding, because when understanding is incomplete, whatever be the practice, it will not be able to bring the required result. There is no use merely complaining, 'I have practiced and practiced and meditated and meditated for years and years, but nothing comes.' May be it is so, but it cannot yield the desired result because it is based on incorrect understanding of the nature of the object. There is a fundamental error on the part of the mind itself, which has not conceived of Reality properly. You are not able to absorb into your feeling the character of Reality in its completeness. And much time may have to be spent even in understanding what It is. Perhaps, the major part of one's life goes only in study and understanding the character of that which we are aiming at. Practice is not the difficulty; the difficulty is understanding. And so, the Upaniṣhad says: 'Having understood, you must strive for realisation.' Such is the nature of what the ancients call a Brāhmaṇa. Nᾱnudhyᾱyᾱd bahῡn śabdᾱn: 'Too much reading is not necessary.' Vᾱco viglᾱpanaṁ hi tat iti: 'It is a mere weariness of speech.'

   So, this is a practical advice, a serious admonition which the Fourth Chapter of the Upaniṣhad gives us as a kind of sequel to its main gospel. Now, we are coming to the close of this chapter, which winds up its teaching by pronouncing its great message. According to the renowned commentator Achārya Śankara, these little passages that follow are the essence of the whole Upaniṣhad. It is a pronouncement of a final judgment, as it were, which the Upaniṣhad gives as a quintessence of its teaching, the message of the whole of the Upaniṣhad. It is short, but very profound.

22. sa vᾱ eṣa mahᾱn aja ᾱtmᾱ yo'yaṁ vijñᾱnamayaḥ prᾱṇeṣu; ya eso'ntar-hṛdaya ᾱkᾱśaḥ tasmin śete, sarvasya vaśī, sarvasyeśᾱnaḥ, sarvasyᾱdhipatiḥ; sa na sᾱdhunᾱ karmaṇᾱ bhῡyᾱn no evᾱsᾱdhunᾱ kanīyᾱn. eṣa sarveśvaraḥ, eṣa bhῡtᾱdhipatiḥ, eṣa bhῡtapᾱlaḥ. eṣa setur vidharaṇa eṣᾱṁ lokᾱnᾱm asambhedᾱya. tam etaṁ vedᾱnuvacanena brᾱhmaṇᾱ vividiṣanti,  yajñena, dᾱnena, tapasᾱnᾱśakena; etam eva viditvᾱ munir bhavati, etam eva pravrᾱjino lokam icchantaḥ pravrajanti. etadd ha sma vai tat pῡrve vidvᾱṁsaḥ prajᾱṁ na kᾱmayante: kiṁ prajayᾱ kariṣyᾱmaḥ; yeṣᾱṁ no'yam ᾱtmᾱyaṁ loka iti. te ha sma putraiṣaṇᾱyᾱś ca vittaiśaṇᾱyᾱś ca lokaiṣaṇᾱyaś ca vyutthᾱya, atha bhikṣᾱ-caryaṁ caranti; yᾱ hy eva putraiṣaṇᾱ sᾱ vittaiṣaṇᾱ, yᾱ vittaiṣaṇᾱ sᾱ lokaiṣaṇᾱ; ubhe hy ete eṣaṇe eva bhavataḥ sa eṣa neti nety ᾱtmᾱ; agṛhyaḥ, na hi gṛhyate; aśīryah, na hi śīryate; asaṅgaḥ, na hi sajyate; asito na vyathate, na riṣyati; etam u haivaite na tarata iti, ataḥ pᾱpam akaravam iti, ataḥ kalyᾱṇam akaravam iti; ubhe u haivaiṣa ete tarati, nainaṁ kṛtᾱkṛte tapataḥ.

This is a longish passage, a single sentence, as it were, which tells us that the practice of spirituality is a double endeavour on the part of the individual to grasp something and renounce something at the same time. It is the renunciation of all finite attachments and a grasping of the nature of the unity of things, a blend of Vairāgya and Ābhyāsa, renunciation and practice.

'This great Being, Mahan Aja, is the Ātman, or the Self of beings.' Sa vᾱ eṣa mahᾱn aja ᾱtmᾱ: 'This immortal great Reality is the Self of all beings', a very interesting sentence. It is the great Reality; It is also the inner Self of all beings. You should not forget this aspect. It is not an extra-cosmic creator of the universe; it is not a transcendent God who is above our heads. It is at once the Ātman, our very Being, our very Self, and the very Existence of all things. It is the immortal Being which is also the Self of things. Yo'yaṁ vijñᾱnamayaḥ prᾱṇeṣu: 'It is manifested as the light in one's own intellect, in one's own reason, in one's own understanding. The little light that peeps through our intellect is this great Light of Being.' It is luminous in one's own heart as the deepest conscience. The heart that you speak of generally, the feeling that you speak of, the conscience that you speak of, is the Hṛdaya of the Upaniṣhad. It is cosmic in its nature. The little heart of yours which appears to be encased in the body is really cosmic in its nature. It is all-pervading. The little ether in the body is very much like the cosmic ether. The little space inside a small vessel is not distinguishable from the vast ether outside, as we all very well know. Likewise is this little peeping, twinkling consciousness - ether in our own hearts, indistinguishable from the consciousness ether of the Absolute outside. The comparison is very interesting and very apt, of course. The space within a little tumbler is indistinguishable from, not different from, the vast space outside. The distinction between the two is only apparent; it is not real. It is only the walls of the vessel that make us feel that there is a distinction between the space within and the space without. There is no such thing as space within and space without. It is an impartite all-comprehensive expanse. So is the consciousness which is the ether of our hearts. So, this ether of the heart within us, the little space within, which is twinkling with the light of intelligence in our own selves, is identical with the Universal Light.