The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
7. And on account of the two conditions of standing and eating (of which the former is characteristic of the highest Lord, the latter of the individual soul).
With reference to that which is the abode of heaven, earth, and so on, the text says, 'Two birds, inseparable friends,' &c. (Mu. Up. III, 1, 1). This passage describes the two states of mere standing, i.e. mere presence, and of eating, the clause, 'One of them eats the sweet fruit,' referring to the eating, i.e. the fruition of the results of works,
and the clause, 'The other one looks on without eating,' describing the condition of mere inactive presence. The two states described, viz. of mere presence on the one hand and of enjoyment on the other hand, show that the Lord and the individual soul are referred to. Now there is room for this statement which represents the Lord as separate from the individual soul, only if the passage about the abode of heaven and earth likewise refers to the Lord; for in that case only there exists a continuity of topic. On any other supposition the second passage would contain a statement about something not connected with the general topic, and would therefore be entirely uncalled for.--But, it may be objected, on your interpretation also the second passage makes an uncalled-for statement, viz. in so far as it represents the individual soul as separate from the Lord.--Not so, we reply. It is nowhere the purpose of Scripture to make statements regarding the individual soul. From ordinary experience the individual soul, which in the different individual bodies is joined to the internal organs and other limiting adjuncts, is known to every one as agent and enjoyer, and we therefore must not assume that it is that which Scripture aims at setting forth. The Lord, on the other hand, about whom ordinary experience tells us nothing, is to be considered as the special topic of all scriptural passages, and we therefore cannot assume that any passage should refer to him merely casually 1.--
[paragraph continues] That the mantra 'two birds,' &c. speaks of the Lord--and the individual soul we have already shown under I, 2, 11.--And if, according to the interpretation given in the Paingi-upanishad (and quoted under I, 2, 11), the verse is understood to refer to the internal organ (sattva) and the individual soul (not to the individual soul and the Lord), even then there is no contradiction (between that interpretation and our present averment that the individual soul is not the abode of heaven and earth).--How so?--Here (i.e. in the present Sûtra and the Sûtras immediately preceding) it is denied that the individual soul which, owing to its imagined connexion with the internal organ and other limiting adjuncts, has a separate existence in separate bodies--its division being analogous to the division of universal space into limited spaces such as the spaces within jars and the like--is that which is called the abode of heaven and earth. That same soul, on the other hand, which exists in all bodies, if considered apart from the limiting adjuncts, is nothing else but the highest Self. Just as the spaces within jars, if considered apart from their limiting conditions, are merged in universal space, so the individual soul also is incontestably that which is denoted as the abode of heaven and earth, since it (the soul) cannot really be separate from the highest Self. That it is not the abode of heaven and earth, is therefore said of the individual soul in so far only as it imagines itself to be connected with the internal organ and so on. Hence it follows that the highest Self is the abode of heaven, earth, and so on.--The same conclusion has already been arrived at under I, 2, 21; for in the passage concerning the source of all beings (which passage is discussed under the Sûtra quoted) we meet with the clause, 'In which heaven and
earth and the sky are woven.' In the present adhikarana the subject is resumed for the sake of further elucidation.
160:1 If the individual soul were meant by the abode of heaven, earth, &c., the statement regarding Îsvara made in the passage about the two birds would be altogether abrupt, and on that ground objectionable. The same difficulty does not present itself with regard to the abrupt mention of the individual soul which is well known to everybody, and to which therefore casual allusions may be made.--I subjoin Ânanda Giri's commentary on the entire passage: Gîvasyopâdhyaikyenâvivakshitatvât tadgñâne#pi sarvagñânasiddhes tasyâyatanatvâdyabhâve hetvantaram vâkyam ity âsankya sûtrena pariharati kutasketyâdinâ. Tad vyâkashte dyubhvâdîti. Nirdesam eva darsayati tayor iti. Vibhaktyartham âha tâbhyâm keti. Sthityesvarasyâdanâg gîvasamgrahe#pi katham îsvarasyaiva visvâyatanatvam tadâha yadîti. Îsvarasyâyanatvenâprakritatve gîvaprithakkathanânupapattir ity uktam eva vyatirekadvârâha anyatheti. Gîvasyâyatanatvenâprakritatve tulyânupapattir iti sankate nanviti. Tasyaikyârtham lokasiddhasyânuvâdatvân naivam ity âha neti. Gîvasyâpûrvatvâbhâvenâpratipâdyatvam eva prakatayati kshetragño hîti. Îsvarasyâpi lokavâdisiddhatvâd apratipâdyatety âsankyâha îsvaras tv iti.