Kena Upanishad 2.p2

2.p2

evaṃ heyopādeyaviparītastvamātmā brahmeti pratyāyitaḥ śiṣyaḥ ahameva brahmeti suṣṭhu vedāhamiti mā gṛhṇīyādityāśayādāhācāryaḥ śiṣyabuddhivicālanārtham--yadītyādi|

Shankara’s Commentary:
Com.—The preceptor, fearing that, the disciple persuaded to believe that lie is the Atman, i.e., the Brahman not fit to be abandoned or acquired, might think ‘I certainly am the Brahman, I know myself well,’ says for the purpose of dispelling that notion of the disciple Yadi, etc. Then, is not an accurate conviction ‘I know (Brahman) well’ desirable? Certainly it is desirable. But an accurate conviction is not of the form ‘I know (Brahman) well.’ If what should be known becomes an object of sense-perception then it is possible to know it well, just as an inflammable substance can be consumed by the consuming fire. But the essence of fire cannot itself be so consumed. The well-ascertained drift of all Vedanta is that the Self (Atman) of every knower is the Brahman. The same has been here explained in the form of question and answer by the text ‘It is the ear of the ear, etc.’ The same has been still more clearly determined by the text: “What is not enlightened by speech, etc.” The traditional theory of those who know the Brahman has also been declared by tbe text: “It is something different from both the known and the unknown.” This Upanishad will also conclude by saying “It is unknown to those who know, and known to those who do not know.” It is, therefore, certainly proper that the notion of the disciple, ‘I know Brahman well’ should be dispelled. It is evident that the knower cannot be known by tbe knower, just as fire cannot be consumed by fire. There is no knower other than th e Brahman, to whom the Brahman can be a knowable, distinct from himself. By the Sruti: “There is no knower other than that,” the existence of another knower is denied. The belief, therefore, ‘I know Brahman well’ is an illusion. Therefore well did the preceptor say ‘Yadi, etc.’