The splendor that is in the sun, which illumines the entire world, and that which is in the moon and in fire, know that splendor as Mine.

Kṛṣṇa reveals His presence in the luminaries. The tejas (splendor, luminous energy) of the āditya (sun) — which bhāsayate (illumines) the jagat (world) akhila (complete) — is His.

So too the tejas of candra (moon) and agni (fire). These three represent the sources of material light. Kṛṣṇa says māmakam — “mine,” not “another’s.” He is the adhiṣṭhātṛ (inner sustainer) of all light. This is different from being identical to the sun; it is the power that makes the sun shine.