तदाहुर्यद्ब्रह्मविद्यया सर्वं भविष्यन्तो मनुष्या मन्यन्ते ।किमु तद्ब्रह्मावेद्यस्मात्तत्सर्वमभवदिति ॥बृह. १,४.९ ॥
In plain words
Here men say: "Since men think that by the knowledge of Brahman they will become all, what then did that Brahman know by which it became all?"
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
यदि किमपि विज्ञायैव तद्ब्रह्म सर्वमभवत् , पृच्छामः — किमु तद्ब्रह्मावेद्यस्मात्तत्सर्वमभवदिति । एवं चोदिते सर्वदो-
In plain words
If Brahman became all by knowing some specific object, we ask: what was that Brahman knowing which it became everything? When the question is put thus, free from every flaw...
Close to the Sanskrit
If Brahman became all simply by knowing something else, we ask: what was that Brahman knowing which it became all? When this is urged, the answer free from all faults...