The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
10. And on account of the topic under discussion.
That the highest Self only can be the eater referred to
is moreover evident from the passage (Ka. Up. I, 2, 18), ('The knowing Self is not born, it dies not'), which shows that the highest Self is the general topic. And to adhere to the general topic is the proper proceeding. Further, the clause, 'Who then knows where he is,' shows that the cognition is connected with difficulties; which circumstance again points to the highest Self.