Measuring others by himself, the highest yogi sees every joy and pain as his own.

Advaita Vedānta

The even vision rests on the actual oneness of the Self. Because the same non-dual Self is the reality of all beings, seeing all happiness and pain as equal is simply seeing truly. One commentator anchors this in right vision: the yogi is harmless because he is established in the correct seeing of the one Self everywhere. The fullest treatment here pushes much deeper. It distinguishes a lesser yogi from the highest yogi even among those who have the knowledge of reality: one who, lacking the destruction of the mind and the wearing-away of mental impressions, is still distracted and tastes visible sorrow while the body lasts attains isolation only at death and is the lesser; but one who has joined knowledge of reality with the destruction of the mind and the wearing-away of impressions tastes the happiness of liberation-in-life now, rises from absorption free of hatred and attachment, and so sees the joy and pain of every being as equal to his own. This commentator lays out a whole discipline of wearing away impressions through cultivated attitudes (friendliness toward the happy, compassion toward the sorrowful, gladness toward the meritorious, equanimity toward the sinful), so that attachment, aversion, and remorse fall away and the mind becomes clear; the verse, on this reading, is the portrait of the one in whom that work is complete.

Śaṅkarācārya · Madhusūdana Sarasvatī · Śrī Nīlakaṇṭha · Dhanapati Sūri

Viśiṣṭādvaita

The likeness is not the identity of all selves but their similarity: each self has the same single essential form, namely unconstricted knowledge, and the selves are alike in being not truly connected to the fortunes of the body. So the yogi sees the happiness that comes as the birth of a son and the pain that comes as a death, in his own self and in all others, as the same. One commentator gives the striking image that he sees the birth, death, and the rest of another's son exactly as he sees those of his own son. This is the consummation of yoga reached even when strong pain-causes come on: the changes of fortune that arrive along the gradient of one's past action and knowledge, once felt as the same in oneself and in another, no longer act as sources of agitation. The verse thus extends sameness of vision into the ethical field, turning inner equality into an outward stance of neither hating nor being hated, neither inflicting nor receiving harm by aversion.

Rāmānujācārya · Vedānta Deśika

Bhedabheda

This commentator reads the likeness plainly: aupamya is the state of being a comparison, so 'by likeness to oneself' means the yogi sees pleasure or pain as the same everywhere on the simple ground that as my pleasure is dear to me, theirs is dear to them, and as my pain is unwelcome to me, so is theirs to them. He sets this verse within the larger teaching of the vision of non-duality everywhere, while noting that such knowledge is exceedingly hard to win.

Śrī Bhāskara

Dvaita

These commentators read the verse as deliberately re-explaining the 'seeing the same everywhere' of an earlier verse (5.29) in a different way, in order to show that an over-reading of that earlier sameness is unsound. One of them notes that when scripture says 'one who sees the same,' a question naturally arises whether this amounts to right seeing in the strict sense, and that the earlier verse was already explained as being established in the Lord; here the sameness is explained as having for its object also the devotee who follows the Lord. The likeness, then, is read carefully so as not to flatten real distinctions among selves and between the soul and God.

Madhvācārya · Śrī Jayatīrtha

Śuddhādvaita

The even vision is not a moral resolve but the natural outflow of devotional seeing (pushti). One commentator ties the sameness to its devotional ground: the yogi sees Vasudeva as the very content of every other being, so equal vision is simply the recognition of the Lord in all. The other develops this through the language of rasa: as for the devotee himself there is joy in the relish of union (sanyoga-rasa) and sorrow in the relish of separation (viyoga-rasa), so he sees the joy or sorrow of every soul as the same, knowing all souls as the merest particles of his own devotional being and as ripples of the Lord's play (leela). Equal vision here is not a flattening into indifference but a Vraja-eyed reading in which every creature's joy and pain is tasted as a movement within the Lord's love.

Vallabhācārya · Śrī Puruṣottama

Kashmir Shaivism

This commentator reads the verse as simple description, not a new command. To see everyone's pleasure and pain as on a par with one's own is just to state the inherent own-form, the natural way of being, of such a yogi; it is not a fresh injunction laid on him from outside. The equality is what he already is, not a duty added to him.

Ācārya Abhinavagupta

Bhakti

These devotional commentators read the verse as the natural ethical outflow of equal vision among those who worship the Lord, where the compassionate yogi is the foremost. Because the one Self of all has been seen, harming any single being becomes the unthinkable thing; the yogi wishes happiness alone for all and sorrow for none. Two of them sharpen the point by contrasting this highest yogi with one who sees the joys and sorrows of self and other unevenly: that uneven seer, even though he be a knower of truth, is not the highest. One of them carries the sameness to its fullest reach, picturing a yogi who views the whole universe, moving and unmoving, as himself, whose mind draws no line between pain and pleasure or auspicious and inauspicious, to whom all three worlds appear as his own form; even while bodied and seemingly subject to pleasure and pain, he is truly the very form of the Supreme. Krishna, on this reading, urges Arjuna to develop exactly this evenness, since there is nothing higher to attain in the universe.

Śrīdhara Svāmī · Śrīla Viśvanātha · Śrīla Baladeva · Sant Jñāneśvar

Modern

These commentators agree on the harmless, all-loving content of the verse but place it differently. One reads it through the lens of action: the idea of one Self in all creation is shared by the paths of knowledge and of meditative discipline, but those paths, favoring renunciation of action, never put this equability to work in life; the karma-yogin of the Gita, by contrast, continually carries this equability of reason, won through realization, into the everyday affairs of the world for universal welfare, which is why this chapter soon ranks him above the ascetic and the scholar. Another reads the verse as the natural conduct of the one earlier called brahma-bhuta, the soul become Brahman, whose delight is by its very nature found in the welfare of all beings. A third dwells on the warmth of it: such a yogi harms no one, wishes good to all, is compassionate to every creature, has a very soft and large heart, and sees this reality everywhere because he is established in the unity of the Self.

Lokmanya Tilak · Swami Sivananda · Swami Ramsukhdas