Kena Upanishad 4.4.p2

4.4.p2

athavā vidyutaḥ ’tejaḥ’ ityadhyāhāryam| vyadyutad vidyotitavat ā 3 iva vidyutastejaḥ

Tasya of the Brahman under discussion, eṣaḥ ādeśaḥ, this is the instruction through analogy. That analogy through which the instruction about the incomparable Brahman is imparted is called ādeśaḥ. What is that? Yat etat, that fact, which is well known among people as the flash of lightning. Since vidyutaḥ vyadyutat, cannot mean that Brahman (vyadyutat) flashed (by borrowing Its light) (vidyutaḥ) from lightning,footnote{"The meaning, 'It flashed from lightning', is inadmissible, for Brahman being self-effulgent, Its effulgence cannot be dependent on others. The meaning, 'It performed the flashing of lightning,' is unacceptable, since the flash that belongs to something cannot be produced by another."—A.G.} therefore the meaning has to be assumed to be "the flash of lightning". Ā, like, is used in the sense of comparison. The meaning is: "It is like the flash of lightning"; and (this meaning is acceptable) since it is seen in a different Vedic text, "comparable to a single flash of lightning" (Bṛ. II. iii. 6); for Brahman disappeared after revealing Itself but once to the gods like lightning. Or the word tejaḥ (brilliance) has to be supplied after the word vidyutaḥ (of lightning). Vyadyutat (in this case) means flashed; (and) ā means as it were. The purport is: It was, as though, the brilliance of lightning flashed but once. The word iti is meant to call back to memory the word ādeśa; (so the meaning is): This is the ādeśa, the analogy. The word it is used for joining together. (So the sense is): Here is another analogy for It. What is that one? Nyamīmiṣat, winked, as the eye did the act of winking. The causative form (in nyamīmiṣat) is used in the same sense as the root itself. The ā is used here, too, in the sense of comparison. The meaning is: And it was like the opening and shutting of the eye with regard to its object. Iti adhidaivatam, this is by way of showing analogies of Brahman in a divine context.