Chapter 13, Verse 18
Part of 13: Kṣhetra Kṣhetrajña Vibhāg Yog — क्षेत्र-क्षेत्रज्ञविभागयोगज्योतिषामपि तज्ज्योतिस्तमसः परमुच्यते।ज्ञानं ज्ञेयं ज्ञानगम्यं हृदि सर्वस्य विष्ठितम्॥
jyotiṣhām api taj jyotis tamasaḥ param uchyate jñānaṁ jñeyaṁ jñāna-gamyaṁ hṛidi sarvasya viṣhṭhitam
That Light of all lights is said to be beyond darkness: knowledge, the knowable, and the goal of knowledge, seated in the hearts of all.
The Supreme Self illumines the intellect, the mind, the sun, moon, stars, fire and lightning. It is selfluminous? The sun does not shine there, nor do the moon and the stars, nor do these lightnings shine and much less this fire. When It shines, everything shines after It all these shine by Its Light. (Kathopanishad 5.15 also Svetasvataropanishad 6.14)Knowledge Such as humility. (Cf. XIII.7to11)The knowable As described in verses 12 to 7. The goal of knowledge, i.e., capable of being understood by wisdom. These three are installed in the heart (Buddhi) of every living being. Though the light of the sun shines in all objects, yet the suns light shines more brilliantly in all bright and clean objects such as a mirror. Even so, though Brahman is present in all objects, the intellect shines with special effulgence received from Brahman. (Cf. X.20XIII.3XVIII.61)