Verse 3.1.1

द्वा सुपर्णा सयुजा सखाया समानं वृक्षं परिषस्वजाते ।
तयोरन्यः पिप्पलं स्वाद्वत्त्यनश्नन्नन्यो अभिचाकशीति ॥ १ ॥

dvā suparṇā sayujā sakhāyā samānaṃ vṛkṣaṃ pariṣasvajāte |
tayoranyaḥ pippalaṃ svādvattyanaśnannanyo abhicākaśīti || 1 ||

1. Two inseparable companions of fine plumage perch on the self-same tree. One of the two feeds on the delicious fruit. The other not tasting of it looks on.

Shankara’s Commentary:

Com.—The Para vidya has been explained, by which the immortal ‘purusa’ or the Truth could be known, by whose knowledge the cause of Samsara, such as the knot of the heart, etc., can be totally destroyed. Yoga which is the means to the realization of the Brahman has also been explained by an illustration “taking the bow and the rest.” Now the subsequent portion is intended to inculcate the auxiliary helps to that yoga, as truth, etc. Chiefly, the truth is here determined by another mode, as it is extremely difficult to realize it. Here, though already done, a mantra (brief) as an aphorism is introduced for the purpose of ascertaining the absolute entity. Suparnau, two of good motion or two birds; (the “word Suparna” being used to denote birds generally); Sayujau inseparable, constant, companions; Sakhayau, bearing the same name or having the same cause of manifestation. Being thus, they are perched on the same tree (‘same,’ because the place where they could be perceived is identical). ‘Tree’ here means ‘body;’ because of the similitude in their liability to be cut or destroyed. Parishasvajate, embraced; just as birds go to the same tree for tasting the fruits. This tree as is well known has its root high up (i.e., in Brahman) and its branches (prana, etc..) downwards; it is transitory and has its source in Avyakta (maya). It is named Kshetra and in it bang the fruits of the karma of all living things. It is here that the Atman, conditioned in the subtle body to which ignorance, desire, karma and their unmanifested tendencies cling, and Isvara are perched like birds. Of these two so perched, one, i.e., kshetrajna occupying the subtle body eats, i.e., tastes from ignorance the fruits of karma marked as happiness and misery, palatable in many and diversified modes; the other, i.e., tbe lord, eternal, pure, intelligent and free in his nature, omniscient and conditioned by maya does not eat; for, lie is the director of both the eater and the thing eaten, by the fact of Ids mere existence as the eternal witness (of all); not tasting, he merely looks on; for, his mere witnessing is direction, as in the case of a king.