The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
16. (He whose work is this is Brahman), because (the 'work') denotes the world.
In the Kaushîtaki-brâhmana, in the dialogue of Bâlâki and Agâtasatru, we read, 'O Bâlâki, he who is the maker of
those persons, he of whom this is the work, he alone is to be known' (Kau. Up. IV, 19). The question here arises whether what is here inculcated as the object of knowledge is the individual soul or the chief vital air or the highest Self.
The pûrvapakshin maintains that the vital air is meant. For, in the first place, he says, the clause 'of whom this is the work' points to the activity of motion, and that activity rests on the vital air. In the second place, we meet with the word 'prâna' in a complementary passage ('Then he becomes one with that prâna alone'), and that word is well known to denote the vital air. In the third place, prâna is the maker of all the persons, the person in the sun, the person in the moon, &c., who in the preceding part of the dialogue had been enumerated by Bâlâki; for that the sun and the other divinities are mere differentiations of prâna we know from another scriptural passage, viz. 'Who is that one god (in whom all the other gods are contained)? Prâna and he is Brahman, and they call him That' (Bri. Up. III, 9, 9).--Or else, the pûrvapakshin continues, the passage under discussion represents the individual soul as the object of knowledge. For of the soul also it can be said that 'this is the work,' if we understand by 'this' all meritorious and non-meritorious actions; and the soul also, in so far as it is the enjoyer, can be viewed as the maker of the persons enumerated in so far as they are instrumental to the soul's fruition. The complementary passage, moreover, contains an inferential mark of the individual soul. For Agâtasatru, in order to instruct Bâlâki about the 'maker of the persons' who had been proposed as the object of knowledge, calls a sleeping man by various names and convinces Bâlâki, by the circumstance that the sleeper does not hear his shouts, that the prâna and so on are not the enjoyers; he thereupon wakes the sleeping man by pushing him with his stick, and so makes Bâlâki comprehend that the being capable of fruition is the individual soul which is distinct from the prâna. A subsequent passage also contains an inferential mark of the individual soul, viz. 'And as the master feeds with his people, nay, as his people feed on the master, thus does this conscious Self feed with
the other Selfs, thus those Selfs feed on the conscious Self' (Kau. Up. IV, 20). And as the individual soul is the support of the prâna, it may itself be called prâna.--We thus conclude that the passage under discussion refers either to the individual soul or to the chief vital air; but not to the Lord, of whom it contains no inferential marks whatever.
To this we make the following reply.--The Lord only can be the maker of the persons enumerated, on account of the force of the introductory part of the section. Bâlâki begins his colloquy with Agâtasatru with the offer, 'Shall I tell you Brahman?' Thereupon he enumerates some individual souls residing in the sun, the moon, and so on, which participate in the sight of the secondary Brahman, and in the end becomes silent. Agâtasatru then sets aside Bâlâki's doctrine as not referring to the chief Brahman--with the words, 'Vainly did you challenge me, saying, Shall I tell you Brahman,' &c.--and proposes the maker of all those individual souls as a new object of knowledge. If now that maker also were merely a soul participating in the sight of the secondary Brahman, the introductory statement which speaks of Brahman would be futile. Hence it follows that the highest Lord himself is meant.--None, moreover, but the highest Lord is capable of being the maker of all those persons as he only is absolutely independent.--Further, the clause 'of whom this is the work' does not refer either to the activity of motion nor to meritorious and non-meritorious actions; for neither of those two is the topic of discussion or has been mentioned previously. Nor can the term 'work' denote the enumerated persons, since the latter are mentioned separately--in the clause, 'He who is the maker of those persons'--and as inferential marks (viz. the neuter gender and the singular number of the word karman, work) contradict that assumption. Nor, again, can the term 'work' denote either the activity whose object the persons are, or the result of that activity, since those two are already implied in the mention of the agent (in the clause, 'He who is the maker'). Thus there remains no other alternative than to
take the pronoun 'this' (in 'He of whom this is the work') as denoting the perceptible world and to understand the same world--as that which is made--by the term 'work.'--We may indeed admit that the world also is not the previous topic of discussion and has not been mentioned before; still, as no specification is mentioned, we conclude that the term 'work' has to be understood in a general sense, and thus denotes what first presents itself to the mind, viz. everything which exists in general. It is, moreover, not true that the world is not the previous topic of discussion; we are rather entitled to conclude from the circumstance that the various persons (in the sun, the moon, &c.) which constitute a part of the world had been specially mentioned before, that the passage in question is concerned with the whole world in general. The conjunction 'or' (in 'or he of whom,' &c.) is meant to exclude the idea of limited makership; so that the whole passage has to be interpreted as follows, 'He who is the maker of those persons forming a part of the world, or rather--to do away with this limitation--he of whom this entire world without any exception is the work.' The special mention made of the persons having been created has for its purpose to show that those persons whom Bâlâki had proclaimed to be Brahman are not Brahman. The passage therefore sets forth the maker of the world in a double aspect, at first as the creator of a special part of the world and thereupon as the creator of the whole remaining part of the world; a way of speaking analogous to such every-day forms of expression as, 'The wandering mendicants are to be fed, and then the Brâhmanas 1.' And that the maker of the world is the highest Lord is affirmed in all Vedânta-texts.
271:1 By the Brâhmanas being meant all those Brâhmanas who are not at the same time wandering mendicants.