Śrīla Śrīdhara Svāmī has translated tapo-mayam as “full of knowledge.” The word tapas, generally indicating “austerity,” is derived from the Sanskrit verb tap, whose meaning can be summarized as indicating the various functions of the sun. Tap means “to burn, to shine, to heat and so on.” The Supreme Lord is eternally perfect, and therefore here tapo-mayam does not indicate that His transcendental body is meant for austerities, since austerities are performed by conditioned souls to purify themselves or to acquire a particular power. An omnipotent, perfect being neither purifies Himself nor acquires power: He is eternally pure and all-powerful. Therefore Śrīdhara Svāmī has intelligently understood that in this case the word tapas refers to the illuminating function of the sun and thus indicates that the Lord’s self-effulgent body is omniscient. Light is a common symbol of knowledge. The Lord’s spiritual effulgence does not merely illuminate physically, as in the case of a candle or light bulb; more importantly, the Lord’s body illuminates our consciousness with perfect knowledge because the Lord’s effulgence is itself perfect knowledge.
Source:A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Tenth Canto, Chapter 27 – Text 04