BG 13.18

13.18 ज्योतिषाम् of lights? अपि even? तत् That? ज्योतिः Light? तमसः from darkness? परम् beyond? उच्यते is said (to be)? ज्ञानम् knowledge? ज्ञेयम् that which is to be known? ज्ञानगम्यम् attainable by knowledge? हृदि in the heart? सर्वस्य of all? विष्ठितम् seated.Commentary 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)

— vedicscriptures · exposition · source ↗

The Supersoul, the Supreme Personality of Godhead, is the source of light in all luminous objects like the sun, moon and stars. In the Vedic literature we find that in the spiritual kingdom there is no need of sun or moon, because the effulgence of the Supreme Lord is there. In the material world that brahma-jyotir, the Lord’s spiritual effulgence, is covered by the mahat-tattva, the material elements; therefore in this material world we require the assistance of sun, moon, electricity, etc., for light. But in the spiritual world there is no need of such things. It is clearly stated in the Vedic literature that because of His luminous effulgence, everything is illuminated. It is clear, therefore, that His situation is not in the material world. He is situated in the spiritual world, which is far, far away in the spiritual sky. That is also confirmed in the Vedic literature. Āditya-varṇaṁ tamasaḥ parastāt ( Śvetāśvatara Upaniṣad 3.8). He is just like the sun, eternally luminous, but He is far, far beyond the darkness of this material world. His knowledge is transcendental. The Vedic literature confirms that Brahman is concentrated transcendental knowledge. To one who is anxious to be transferred to that spiritual world, knowledge is given by the Supreme Lord, who is situated in everyone’s heart. One Vedic mantra ( Śvetāśvatara Upaniṣad 6.18) says, taṁ ha devam ātma-buddhi-prakāśaṁ mumukṣur vai śaraṇam ahaṁ prapadye. One must surrender unto the Supreme Personality of Godhead if he at all wants liberation. As far as the goal of ultimate knowledge is concerned, it is also confirmed in Vedic literature: tam eva viditvāti mṛtyum eti. “Only by knowing Him can one surpass the boundary of birth and death.” ( Śvetāśvatara Upaniṣad 3.8) He is situated in everyone’s heart as the supreme controller. The Supreme has legs and hands distributed everywhere, and this cannot be said of the individual soul. Therefore that there are two knowers of the field of activity – the individual soul and the Supersoul – must be admitted. One’s hands and legs are distributed locally, but Kṛṣṇa’s hands and legs are distributed everywhere. This is confirmed in the Śvetāśvatara Upaniṣad (3.17): sarvasya prabhum īśānaṁ sarvasya śaraṇaṁ bṛhat. That Supreme Personality of Godhead, Supersoul, is the prabhu, or master, of all living entities; therefore He is the ultimate shelter of all living entities. So there is no denying the fact that the Supreme Supersoul and the individual soul are always different.

— vedicscriptures · exposition · source ↗