When knowledge destroys ignorance, the supreme reality it had hidden stands revealed, the way the sun lights what was already there.

Advaita Vedānta

Knowledge here is the discriminating realization of the non-dual Self as Brahml, summed up in the great-sentence taught by the guru, 'I am Brahman.' These commentators treat ignorance as something positive, not a mere blank absence of knowledge. The reasoning is precise: the verse says ignorance is what 'veils' and what is 'destroyed' by knowledge, and a sheer absence could neither veil anything nor be destroyed; so the ignorance witnessed in 'I am ignorant, I do not know myself' must be a positive, beginningless, indescribable power called maya, possessing two functions, veiling and projecting. The veiling is twofold: one kind makes the existent seem non-existent and yields to any valid knowledge, while the deeper kind makes the self-luminous seem non-shining and yields only to the direct, concept-free realization born of the Vedanta-sentence. That realizing knowledge, like the sun, by its mere arising removes ignorance together with all its effects, needing no co-factor, and reveals the one Self without a second, of the nature of being, consciousness, bliss and the endless.

Śaṅkarācārya · Śrī Ānandagiri · Madhusūdana Sarasvatī · Śrī Nīlakaṇṭha · Dhanapati Sūri

Viśiṣṭādvaita

Knowledge is not the self's whole substance but a property that belongs to the self, attendant on its very nature, as light belongs to the sun. These commentators read 'their' (the plural) very pointedly: Krishna speaks of those selves, in the plural, and this shows that selves are genuinely many. That plurality is not produced by limiting adjuncts, for in those whose ignorance is destroyed there is not a trace of any adjunct left, yet the plural still stands. This confirms what was said at the Gita's opening, that 'never was there a time when I was not, nor you, nor these.' The sun-and-its-light image is used to show how knower and knowledge co-abide: just as sun and its light remain distinct yet together, so the self and its knowledge remain distinct yet together. This is also why knowledge can be 'contracted' by action in bondage and 'unfold' fully in liberation. The supreme self that is revealed is shown in its own nature, not as conditioned by any adjunct, and the freedom from doership argued earlier is one of the very things this knowledge manifests.

Rāmānujācārya · Vedānta Deśika

Dvaita

These commentators raise and answer a sharp objection: it is obvious that knowledge destroys ignorance and reveals its object, so why state it again here? The answer is that 5.15 had said knowledge itself is 'covered by ignorance,' which seems to make liberation impossible: if the very knowledge that should save us is itself buried, then either it can never be uncovered, or some other agent must do the uncovering, which would make renunciation and yoga (whose whole aim is knowledge) pointless. The resolution is to distinguish two knowledges. The knowledge that is the soul's own essential nature is what gets covered by ignorance; but a second knowledge, a mental modification, is what loosens that covering and reveals Brahman. The verse marks this second one. On this reading the word in the instrumental ('by knowledge') denotes specifically the second, immediate, direct knowledge, not the first indirect one; otherwise the two separate mentions of knowledge would be redundant. The single-sun-does-both reading (one knowledge that both destroys ignorance and reveals the supreme) is explicitly rejected as unsound.

Madhvācārya · Śrī Jayatīrtha

Śuddhādvaita

The saving knowledge is a gift, not the soul's own achievement. These commentators stress that those who do not fall into delusion are precisely those who have 'received' the knowledge of the self given by the Lord himself, the rare recipients of grace and objects of his compassion. The knowledge by which ignorance is destroyed is itself of the Lord's own form, made of the supreme Brahman, and so it carries an apparent independent agency of its own ('that knowledge is itself the agent'). What is given comes bearing the very signature of the giver. The Upanishadic word 'the knower of Brahman attains the highest' is brought in to confirm what is revealed; and the sun simile is read in full, the sun driving darkness far off and making manifest the whole array of things together with its own self.

Vallabhācārya · Śrī Puruṣottama

Kashmir Shaivism

Once ignorance is destroyed by knowledge, the self-and-other-revealing power of knowledge stands established of itself, just as the sun's revealing power is established of itself once darkness is gone. The stress is on this self-establishing: knowledge needs no separate help to do its revealing work. The reading is condensed in an image: with the suspicion (the wrong fear or doubt) turned back, the nectar by itself does the work of nectar. That is, once the obstruction is removed, the true nature simply acts as its own nature, revealing both itself and all else.

Ācārya Abhinavagupta

Bhakti

The self that is known is the self who is Bhagavan, the supreme Lord, and the perfect, all-full divine nature (Isvara-svarupa) is what stands revealed. These commentators read knowledge as the Lord's own power. One stresses that ignorance and knowledge are properties of material nature alone, which is what actually binds and liberates; the Lord himself binds and frees no one, and acts only as the indweller who awakens these properties, so there is no partiality or cruelty in him. Another describes the destroyed ignorance specifically as the soul's 'aversion toward him,' and says knowledge awakens the devotee to the living soul as beyond the body and to the Lord as free of faults like partiality. Reading 'their' in the plural, this voice (like the Vishishtadvaita reading) takes the manyness of liberated souls as real and refutes the idea that it is merely the work of limiting adjuncts. The Marathi voice draws out the lived sequence: when ignorance dissolves comes the vision of God as the true non-doer, then the realization 'I am that very God,' and then the seer views the whole world as rooted in the essence of the Self, just as the risen sun does not light only the eastern sky while the rest stays dark.

Śrīdhara Svāmī · Śrīla Viśvanātha · Śrīla Baladeva · Sant Jñāneśvar

Modern

This voice renders the verse in plain experiential terms. Ignorance is taking the changing body and the unchanging self to be one and the same; knowledge (here called viveka, discernment) is clearly seeing them as distinct. The proof offered is from ordinary experience: we plainly notice that our I-ness and mine-ness keep changing (first a child with toys, then grown with spouse, wealth, house), yet our own bare existence (satta) never changes or disappears. The seeker is told to give weight to this discernment and so loosen the false bond between the unchanging self and the changing things. When that discernment is fully awakened and the changing is set aside, a clear knowing of one's own true nature dawns, and at once the all-pervading supreme reality (paramatma-tattva) is experienced everywhere as non-different from oneself. 'Prakashayati' is read just as with the sun: when the sun rises nothing new is made; the thing that was there but hidden simply begins to be seen. So too the supreme reality is naturally already established; ignorance only kept it from being experienced, and removing ignorance lets that ever-present reality come into direct experience.

Swami Ramsukhdas · Swami Sivananda · Lokmanya Tilak