Advaita Vedānta

For these commentators the supremacy of knowledge follows directly from its unique power to end ignorance, which is the very root of bondage. They frame the verse against an objector who asks: if some other purifier, such as the great horse-sacrifice, could reach the supreme human goal, why bother with Self-knowledge at all? The answer is that whatever does not remove ignorance cannot remove sin at its root; the cause persists and sin rises again, so no rite can equal knowledge. They take 'in the Self' to mean the realization arises in one's own inner organ, and they stress that the teacher and the Veda can only give mediate, conceptual knowledge, while the direct realization of the indivisible Self must be won by oneself; the long time required is simply the time needed to attain fitness, which most have not yet reached.

Śaṅkarācārya · Śrī Ānandagiri · Madhusūdana Sarasvatī · Dhanapati Sūri

Viśiṣṭādvaita

These commentators read knowledge as knowledge of the self that is supremely purifying by its very nature, and they ground its purifying power in scripture: the soul is purified by knowledge of the Lord (citing Yajnavalkya). The knowledge meant is to be 'carried out day by day in accordance with the teaching,' a continuing practice shaped by the scriptural instruction rather than a single flash. They are careful that mere present wishing does not produce it on demand, which is why the verse adds 'of itself' and 'in time': knowledge comes at the maturation-state, when the discipline of action is complete and there is no longer any external prompter needed.

Rāmānujācārya · Vedānta Deśika

Bhedabheda

This commentator reads the verse closely as grammar and process. Knowledge has no equal in purifying power in the matter taught by the scriptures, and he notes that the word for knowledge here itself denotes the Self. The one perfected by the discipline of action finds it 'in the Self,' which he glosses as in one's own understanding, and 'in due course,' with time itself being the cause of ripening. He then turns to mark a distinction the next verse develops: the external occasion for knowledge, such as prostration before a teacher, has been given, and now the internal occasion, faith and restraint of the senses, is to be stated.

Śrī Bhāskara

Dvaita

These commentators do not gloss the verse as an independent statement but read it as a structural hinge. They take Krishna to be rounding off the topic of knowledge and pointing ahead: this verse states the matter in a single utterance, and the following verses then unfold what is meant. They lay out the scheme it introduces: the intimate means to knowledge are faith and the rest, the contrary to it is ignorance and the like, the fruit of knowledge is supreme peace, and the fruit of its opposite is destruction. The verse, on this reading, is the summary line that organizes the verses that follow.

Madhvācārya · Śrī Jayatīrtha

Śuddhādvaita

For these commentators knowledge is the highest purifier, but its final attainment turns on the Lord's grace. Vallabha takes the knowledge praised here to be of one meaning with both sankhya and yoga, and says that even when reached by sankhya it comes to the Self in due time only when yoga is well accomplished; against those who set sankhya and yoga in opposition, he holds them together as the single brahma-knowledge attained by one whom the Lord has favoured. For the Pustimarg the decisive closing note is that the highest knowledge itself is reached only by the Lord's own grace (mat-anugraha). Purushottama reads the seeker as one who has done karma-yoga at the Lord's command, without longing for fruit, for the sake of the Lord's satisfaction, and who in supra-mundane time comes to know the knowledge whose very substance is the Lord's form.

Vallabhācārya · Śrī Puruṣottama

Kashmir Shaivism

This commentator adds a precise reason for knowledge's unique purity. The purity of anything else comes by an addition from outside, borrowed, not belonging to the thing itself; knowledge alone is pure in its own nature. He deliberately declines to spin this point out at length for fear of over-extension. And he gives the realization an experiential turn: this purity is something one will know for oneself when one is well awakened, not merely accepted on report.

Ācārya Abhinavagupta

Bhakti

These commentators set knowledge above austerity, yoga and the rest, and underline that it is not easily available to all. It comes only when the yoga of desireless action is fully perfected, not while unripe, and even then only in time, not at once. Vishvanatha and Baladeva add a pointed caution: it is found within one's own Self, won by oneself, and not by the mere external act of taking up the renounced order; inner ripening, not a change of outward status, is what brings it. Sridhara stresses that when it does come it is attained spontaneously, without strain, yet never apart from karma-yoga. Jnaneshwari pours this into vivid imagery: knowledge can be compared only to knowledge, as the taste of ambrosia can be compared only to ambrosia, and ends by having Krishna promise to disclose the one sure way knowledge can be possessed.

Śrīdhara Svāmī · Śrīla Viśvanātha · Śrīla Baladeva · Sant Jñāneśvar

Modern

These commentators keep the verse plain and practical. Sivananda reads it straight: there is no purifier equal to Self-knowledge, and the one perfected by constant practice of karma-yoga and dhyana-yoga finds it in himself after a time. Tilak ties it back to the previous verse on action: acquiring knowledge through desireless actions begun by one's own reason is the principal means, the path accessible to reason, while those who cannot follow that path are offered the path of faith next. Ramsukhdas dwells on the word 'here' (iha), which he takes to mean the human world specifically, for only in a human body is there the right and the opportunity (adhikara and avasara) for purification; he traces impurity to treating the world as independently real and then explains that when knowledge of reality dawns that false reality ends and great purity sets in, and that all other practices and holy rivers are themselves only means toward this knowledge, which is their goal.

Swami Sivananda · Lokmanya Tilak · Swami Ramsukhdas