Knowledge brings about bondage to freedom

Even though self-knowledge can be known only in the mind, it is not as an object, but as oneself alone. This fact is emphasised in mantra 12 and 13.

aṅguṣṭhamātraḥ puruṣo madhya ātmani tiṣṭhati |

īśāno bhūtabhavyasya na tato vijugupsate |

etadvai tat ||2.1.12||

Ātmā, which is the size of the thumb, (and) which is the lord of the past and the

future, dwells in the heart of the body. After (knowing that), one does not seek

security. This is indeed that.

puruṣo madhya ātmani tiṣṭhati - jīvātmā is (as though) situated in the center

(heart) of the body. puruṣaḥ - consciousness even though it pervades the entire person, but is said to be situated in the buddhi (center of the heart), because its nature of illuminating is fully manifest in the buddhi (as reflected consciousness). Śruti says that this jīvātmā resides in the space in the heart, which is of the size of the thumb - aṅguṣṭhamātraḥ, for the purpose of upāsana.

īśāno bhūtabhavyasya - (this jīvātmā, which is non-different from īśvara) is the lord of the creation - the past, (present) and the future. Even though the individual appears to be limited by time, in nature it is limitless, because there is only one ātmā which appears to be various. Just like the space within the pot is viewed as limited space. Upon enquiry, we understand that the expression limited space is a delusion. We know that the space is neither inside nor outside the pot, but all pots are within the space. In the same way, consciousness is neither within nor without the individual; everything is within consciousness ātmā. After knowing that oneness, na tato vijugupsate - one doesn’t seek security, because he never feels insecure, while everything is me alone.

It is the consciousness that naciketa was seeking in the third boon - etadvai tat.

aṅguṣṭhamātraḥ puruṣo jyotirivādhūmakaḥ |

īśāno bhūtabhavyasya sa evādya sa u śvaḥ |

etadvai tat ||2.1.13||

Ātmā, which is the size of the thumb, (and) which is the lord of the past and the

future, is like a flame without smoke. That alone (exists) today; that alone (will

exist) tomorrow. This is indeed that.

Consciousness is seemingly limited in size and confined to the body as jīvātmā. This is how we experience. We recognise consciousness only in our body and therefore erroneously conclude that it is limited to the periphery of the body, particularly the mind. Śruti likens the jīvātmā to a smokeless flame that is capable of brightly illuminating other objects and itself - jyotirivādhūmakaḥ.

Śastra defines light as that in whose presence things are known. Every sense organ is comparable to light. Only in the presence of the mind, things can be known, and therefore, the mind is also comparable to light. Yet, the ultimate light among those instruments is consciousness, without whose presence, neither the mind nor the sense organs are able to perceive.

That is why jīvātmā is called the light of lights. The light that never switches off, it ever illumines today and the future (including the past) -  sa evādya sa u śvaḥ. This jīvātmā is none other than the paramātmā, the lord of the past, (present) and future - īśāno bhūtabhavyasya.

Thus, it rules out the misconception that consciousness is destroyed along with the death of the body. Śruti says that consciousness alone exists today and that alone will exist in the future. This is a direct answer to naciketas’ question in 1.1.20: “is there any entity that survive death?” It is ātmā, the very self of the individual - etadvai tat.

Once again, śruti negates the vision of duality by showing the result.

yathodakam durge vṛṣṭam parvateṣu vidhāvati |

evam dharmān pṛthak paśyamstānevānuvidhāvati ||2.1.14||

Just as rainwater falling on a mountain peak flows down in different directions,

so one who sees ātmā as different from individuals,  goes after different bodies.

dharmān pṛthak paśyamstānevānuvidhāvati - one who sees ātmā as different from individuals, he will be born again and again in varieties of bodies. To convey this, śruti gives an analogy of rainwater falling on the peak of the mountain. The water divides itself into many streams, scattered and disappeared - yathodakam durge vṛṣṭam parvateṣu vidhāvati. Rainfall on the peak of the mountain conveys that there is only one ātmā which manifests into many jīva (many streams). If one thinks that every individual is different from ātmā, just like the water of each stream is different from the rainwater on the peak, he is also like the stream water, gets scattered and destroyed in this life, again and again attains different bodies.

On the other hand, one who has the knowledge of non-dual ātmā, by understanding the perception of duality is only caused by upādhi, he attains immortality.

yathodakam śuddhe śuddhamāsiktam tādṛgeva bhavati |

evam munervijānata ātmā bhavati gautama ||2.1.15||

Just as pure water poured in pure (water), becomes the same kind alone. Similarly ātmā of a person who is knowing becomes ātmā of a wise sage. Oh naciketa!

Śruti reveals the oneness of all being through an analogy of water. When a container of pure water is poured into another (larger) container of pure water, one water cannot differentiate from another water; they become indistinguishable one - yathodakam śuddhe śuddhamāsiktam tādṛgeva bhavati. Similarly, through proper means, one who abides in self-knowledge, his ātmā becomes ātmā of a wise sage (he knows he is not different from the wise person) - evam munervijānata ātmā bhavati. There is no becoming here, because all along there is just one ātmā. The word “becomes” is just to show that knowledge brings about bondage to freedom.