Bhagavad Gita Chapter 13, Verse 33

यथा प्रकाशयत्येकः कृत्स्नं लोकमिमं रविः | क्षेत्रं क्षेत्री तथा कृत्स्नं प्रकाशयति भारत ||

yathā prakāśayaty ekaḥ kṛtsnaṁ lokam imaṁ raviḥ kṣetraṁ kṣetrī tathā kṛtsnaṁ prakāśayati bhārata

Just as the one sun illuminates this entire world, O descendant of Bharata, so the knower of the field illuminates the entire field.

Krishna uses the analogy of the sun to explain how the knower illuminates the field. 'Yathā prakāśayaty ekaḥ kṛtsnaṁ lokam imaṁ raviḥ'—just as the one sun illuminates this entire world. One sun illuminates everything—no matter how diverse the world is, one sun lights it all. 'Kṣetraṁ kṣetrī tathā kṛtsnaṁ prakāśayati'—so also the knower of the field illuminates the entire field. The knower (consciousness) illuminates the field (the body). Without the knower, the field has no awareness. The knower makes the field conscious. When you understand this, you recognize that you (the knower) illuminate the field. The field is diverse—many parts, many functions. But one knower illuminates it all. Without the knower, the field is inert. With the knower, the field is alive and conscious.