The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut [1890] at sacred-texts.com
10. The Imperishable (is Brahman) on account of (its) supporting (all things) up to ether.
We read (Bri. Up. III, 8, 7; 8). 'In what then is the ether woven, like warp and woof?--He said: O Gârgî, the Brâhmanas call this the akshara (the Imperishable). It is neither coarse nor fine,' and so on.--Here the doubt arises whether the word 'akshara' means 'syllable' or 'the highest Lord.'
The pûrvapakshin maintains that the word 'akshara' means 'syllable' merely, because it has, in such terms as akshara-samâmnâya, the meaning of 'syllable;' because we have no right to disregard the settled meaning of a word; and because another scriptural passage also ('The syllable Om is all this,' Kh. Up. II, 23, 4) declares a syllable, represented as the object of devotion, to be the Self of all.
To this we reply that the highest Self only is denoted by the word 'akshara.'--Why?--Because it (the akshara) is said to support the entire aggregate of effects, from earth up to ether. For the sacred text declares at first that the entire aggregate of effects beginning with earth and differentiated by threefold time is based on ether, in which it is 'woven like warp and woof;' leads then (by means of the question, 'In what then is the ether woven, like warp and woof?') over to the akshara, and, finally, concludes with the words, 'In that akshara then, O Gârgî, the ether is woven, like warp and woof.'--Now the attribute of supporting everything up to ether cannot be ascribed to any being but Brahman. The text (quoted from the Kh. Up.) says indeed that the syllable Om is all this, but that statement
is to be understood as a mere glorification of the syllable Om considered as a means to obtain Brahman.--Therefore we take akshara to mean either 'the Imperishable' or 'that which pervades;' on the ground of either of which explanations it must be identified with the highest Brahman.
But--our opponent resumes--while we must admit that the above reasoning holds good so far that the circumstance of the akshara supporting all things up to ether is to be accepted as a proof of all effects depending on a cause, we point out that it may be employed by those also who declare the pradhâna to be the general cause. How then does the previous argumentation specially establish Brahman (to the exclusion of the pradhâna)?--The reply to this is given in the next Sûtra.