Advaita Vedānta

These commentators concentrate on parsing exactly what is covered and why the enmity is called 'constant' for the knower. Most read the veiled 'knowledge' as viveka-jnana, the discriminating knowledge that distinguishes the real from the unreal. One voice, however, takes 'knowledge' here as the inner organ (the mind itself), understood as the sattva or pure luminous aspect of mind: this sattva is fire-like and illuminating by nature, but desire, which is made of rajas (the restless quality), covers it like smoke and casts the knower into harm; left uncovered, that same pure mind would by discernment and dispassion lift him up. Another of these voices explicitly rejects taking 'knowledge' as the inner organ as a forced reading, insisting that the link to 'knowledge and special knowledge' in the next verse shows discriminating knowledge is meant. They also work to defend the wording 'constant enemy of the knower': desire is intrinsically everyone's enemy, but a sub-distinction is drawn by knowledge and ignorance, so that only for the knower, who recognizes the harm from the very start, is the enmity unbroken.

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

Viśiṣṭādvaita

Here the covered knowledge is specifically atmika-jnana, the knowledge directed at the self, not knowledge of mere objects; the knower is the embodied creature (jantu) whose very nature is knowledge. One commentator is careful to say the 'knower' here is neither the fully realized soul nor one with no knowledge at all, but the conscious being whose knowledge is in the process of becoming. The way desire obstructs is precise: it works by inducing bewilderment toward objects (vishaya-vyamoha). It is the eternal foe so long as the direct vision of the self has not been attained; for the soul caught in endless transmigration this enmity of desire is fixed. The covering is described as happening by way of an adjunct or limiting condition (upadhi), and the fire-image is taken metaphorically, since real fire has its uses but here the point is only that desire, like fire, knows no satiety.

Rāmānujācārya · Vedānta Deśika

Dvaita

These commentators read the verse as making a distinct and stronger point than the previous one, and they ground this in scripture (citing Brahma Sutra 3.4.15, 'and some, by the force of desire'). The earlier verse said desire obstructs knowledge from arising; this verse says that even knowledge that has somehow already arisen from scripture does not, when veiled by desire, shine forth so as to give the direct vision of the supreme Self. So there is no mere repetition. This holds of the man of real scriptural knowledge, and all the more of one with only slight knowledge gained from a teacher's instruction. On why desire is 'hard to fill', they give a vivid escalation: the rank of Indra is not easily won, and even when it is reached one then craves the rank of Brahma, so the thought 'enough' never comes. One of them also pointedly sets aside a rival reading that made desire the enemy 'of the knower, not the fool' on the grounds that the knower fights it while the fool follows it; he argues that real enmity means doing harm, and harm is in fact greater in the fool. They close with a threefold simile from tradition: for the knowledge that is of Brahman, desire is the smoke that veils fire; for the intellect it is the dirt on a mirror; for the living being it is the caul around the embryo.

Madhvācārya · Śrī Jayatīrtha

Śuddhādvaita

These commentators stress that desire scorches the devotee, not only the philosopher. One reads the address 'Kaunteya' as marking the listener as a devotee at root, fit for the teaching, and the 'knower' as one who knows his own form as a portion of the Lord; even his right knowledge is covered by the everlasting foe, desire. He offers a striking gloss on the 'fire' (anala): it can be read as the rasa-cooker, the digestive fire seated in the belly, by which the body's appetites feed and increase desire, so that 'all is conquered when the rasa is conquered'. The other emphasizes that the likening to fire turns on desire's character as a cause of grief and burning: desire scorches the seeker even as it veils him. For this school the verse is read as 'plain', its enmity made stark by the words themselves.

Vallabhācārya · Śrī Puruṣottama

Kashmir Shaivism

This commentator gives a terse but pointed gloss. Desire has 'the form of desire' because it moves in wishing, in the very act of longing. And it is like a fire that can never be filled because it burns up both the seen and the unseen, that is, both this-worldly and other-worldly goods. The point is the totality of what desire consumes: nothing it touches escapes its burning.

Ācārya Abhinavagupta

Bhakti

These commentators read the covered knowledge as viveka-jnana, discriminating knowledge, and draw the friend-versus-foe contrast between the ignorant and the wise to show why desire is the eternal enemy of the wise. They press the practical edge hard: since it is the eternal foe, it is to be slain in every way. One identifies desire outright as the very nescience (ignorance) of the living being, glossing 'in the form of desire' as ignorance wearing the shape of desire; the connective 'and' he takes in the sense of 'as', that is, 'like fire'. Several quote the Bhagavata text (9.19.14) that desire is never appeased by enjoyment but, like the black-trailed fire fed with offerings, only grows greater. One of them adds a sobering observation about the fight itself: knowledge by itself is quite clear but stays a mystery while enveloped by lust and anger, and you cannot simply conquer them first and then gain knowledge, because the very remedies you bring against them tend to feed them, as dry wood fed to a fire only makes it burn higher.

Śrīdhara Svāmī · Śrīla Viśvanātha · Śrīla Baladeva · Sant Jñāneśvar

Bhedabheda

This source does not give a separate exposition; it largely restates the verse. As preserved here it describes desire as the subtle, supreme enemy of embodied beings together with the senses, seated as if at ease and deluding them. The emphasis falls on desire's hidden, settled presence within the embodied being and its senses, working its delusion from within.

Śrī Bhāskara

Modern

Among the modern commentators present here, the emphasis is on the psychology of the insatiable fire and on continuity with the verses just before. One quotes Manu that desire can never be cooled by enjoyment but, like fire fed with ghee and wood, blazes the more, and gives the vivid illustration that if all the food, metals, animals and beautiful people on earth passed to one craving man they would still fail to satisfy him; he also restates the friend-to-the-ignorant, foe-to-the-wise contrast, the wise man knowing from experience, even before the consequence, that desire brings only trouble. Another reads the verse as a deliberate repetition of the same Manu text and ties it back into a karma-yoga reading of the chapter. A third explicitly links 'etena' ('by this') back to the thirty-seventh verse, where Krishna had named kama (here read as kamana, the wishing impulse) as the chief cause that drives a person to sin; the same craving is meant here, and to call it 'anala' is to say it is a fire that can never be filled, growing larger the more it consumes.

Swami Sivananda · Lokmanya Tilak · Swami Ramsukhdas