This shloka completes the first major section of Chapter 15.

From 15.1 to the first half of 15.3, Bhagavān described samsāra as the aśvattha tree. From the second half of 15.3 through 15.5, the means of freedom from samsāra were taught: vairāgyam, śaraṇāgati, sadguṇāḥ, and Vedānta-vicāraḥ. By following these, the seeker becomes amūḍhaḥ, a wise person, and attains tad avyayaṃ padam, the imperishable Brahman. Now, in 15.6, that Brahman is defined.

This is an important definition, based on well-known Upaniṣadic mantras from the Kaṭhopaniṣad and Muṇḍakopaniṣad: na tatra sūryo bhāti na candra-tārakam — there the sun does not shine, nor the moon and stars. The Gītā presents the same teaching in its own form: na tad bhāsayate sūryaḥ, na śaśāṅkaḥ, na pāvakaḥ — the sun does not illumine That; neither the moon nor fire.

At first, this may sound like a description of some faraway place where ordinary light does not reach. But the teaching is subtler. Brahman is not being described as a dark physical location beyond the sun and moon. Brahman is being defined as pure consciousness, the self-effulgent awareness because of which everything else is known.

The sun illumines objects outside during the day. The moon illumines gently at night. Fire or lamp illumines objects in a room. But all these lights reveal only objects. Even when the sun shines, I must be conscious to know the sunlight. Even when a lamp is lit, I must be conscious to know the lamp. Even when a thought rises in the mind, I must be conscious to know that thought.

Therefore consciousness is not illumined by the sun, moon, or fire. Rather, the sun, moon, fire, body, mind, senses, thoughts, and experiences are all known because of consciousness. Brahman is that consciousness.

This is why Brahman is called the unobjectifiable subject. Everything else can become an object of knowledge. I can know a pot, a sound, a color, a feeling, a memory, a thought, or even the absence of a thought. But the knower of all these cannot be turned into one more object. The eye can see forms, but it cannot see itself directly as an object without a mirror. Consciousness knows all objects, but consciousness itself is never known as an object. It is the very subject because of which all knowing takes place.

In simple language: Brahman is the light because of which every experience is known. It is not a light like a bulb or the sun. It is the light of awareness. Physical light removes physical darkness. Consciousness reveals both light and darkness. It reveals waking experiences, dream experiences, and even the peaceful blankness of deep sleep later recognized as “I slept well.”

The verse says tad dhāma paramaṃ mama — That is My supreme dhāma. Here dhāma should not be reduced to a physical abode or heavenly address. It means Bhagavān’s supreme nature, the higher reality. Earlier, Chapter 7 spoke of Bhagavān’s higher and lower nature: the lower nature is the changing, saguṇa, material order; the higher nature is consciousness. Here Bhagavān points to that supreme nature, paramaṃ dhāma, as Brahman itself.

The verse also repeats the result: yad gatvā na nivartante — having attained which, they do not return. This does not mean travelling to a place and being prevented from returning. It means that once Brahman is known as one’s own real nature, the fundamental error is removed. Mokṣa is not a physical event of going somewhere; it is the dropping of the wrong notion that I, the jīvātma, am away from Brahman. In Vedānta, knowledge and mokṣa are closely connected because wrong notion is removed only by right knowledge.

So 15.6 gives the definition of the imperishable padam mentioned in 15.5. Brahman is not an object illumined by something else. Brahman is self-effulgent consciousness, the witness because of which all objects, lights, thoughts, and experiences are known. Knowing that as one’s own higher nature is mokṣa.