The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
18. The internal ruler over the devas and so on (is Brahman), because the attributes of that (Brahman) are designated.
In Bri. Up. III, 7, 1 ff. we read, 'He who within rules this world and the other world and all beings,' and later on, 'He who dwells in the earth and within the earth, whom
the earth does not know, whose body the earth is, who rules the earth within, he is thy Self, the ruler within, the immortal,' &c. The entire chapter (to sum up its contents) speaks of a being, called the antaryâmin (the internal ruler), who, dwelling within, rules with reference to the gods, the world, the Veda, the sacrifice, the beings, the Self.--Here now, owing to the unusualness of the term (antaryâmin), there arises a doubt whether it denotes the Self of some deity which presides over the gods and so on, or some Yogin who has acquired extraordinary powers, such as, for instance, the capability of making his body subtle, or the highest Self, or some other being. What alternative then does recommend itself?
As the term is an unknown one, the pûrvapakshin says, we must assume that the being denoted by it is also an unknown one, different from all those mentioned above.--Or else it may be said that, on the one hand, we have no right to assume something of an altogether indefinite character, and that, on the other hand, the term antaryâmin--which is derived from antaryamana (ruling within)--cannot be called altogether unknown, that therefore antaryâmin may be assumed to denote some god presiding over the earth, and so on. Similarly, we read (Bri. Up. III, 9, 16), 'He whose dwelling is the earth, whose sight is fire, whose mind is light,' &c. A god of that kind is capable of ruling the earth, and so on, dwelling within them, because he is endowed with the organs of action; rulership is therefore rightly ascribed to him.--Or else the rulership spoken of may belong to some Yogin whom his extraordinary powers enable to enter within all things.--The highest Self, on the other hand, cannot be meant, as it does not possess the organs of action (which are required for ruling).
To this we make the following reply.--The internal ruler, of whom Scripture speaks with reference to the gods, must be the highest Self, cannot be anything else.--Why so?--Because its qualities are designated in the passage under discussion. The universal rulership implied in the statement that, dwelling within, it rules the entire aggregate of created beings, inclusive of the gods, and so on, is an appropriate
attribute of the highest Self, since omnipotence depends on (the omnipotent ruler) being the cause of all created things.--The qualities of Selfhood and immortality also, which are mentioned in the passage, 'He is thy Self, the ruler within, the immortal,' belong in their primary sense to the highest Self.--Further, the passage, 'He whom the earth does not know,' which declares that the internal ruler is not known by the earth-deity, shows him to be different from that deity; for the deity of the earth knows itself to be the earth.--The attributes 'unseen,' 'unheard,' also point to the highest Self, which is devoid of shape and other sensible qualities.--The objection that the highest Self is destitute of the organs of action, and hence cannot be a ruler, is without force, because organs of action may be ascribed to him owing to the organs of action of those whom he rules,--If it should be objected that [if we once admit an internal ruler in addition to the individual soul] we are driven to assume again another and another ruler ad infinitum; we reply that this is not the case, as actually there is no other ruler (but the highest Self 1). The objection would be valid only in the case of a difference of rulers actually existing.--For all these reasons, the internal ruler is no other but the highest Self.
132:1 According to Scripture, Nirankusam sarvaniyantritvam srautam na ka tâdrise sarvaniyantari bhedo na kânumânam srutibhâditam uttishthati. Ânanda Giri. Or else, as Go. Ân. remarks, we may explain: as the highest Self is not really different from the individual soul. So also Bhâmatî: Na kânavasthâ, na hi niyantrantaram tena niyamyate kim tu yo gîvo niyantâ lokasiddhah sa paramâtmevopâdhyavakkhedakalpitabhedah.