SRIMAD-BHAGAVATAM 7 CHAPTER 15 TEXT 57
ādāv ante janānāṁ sad
bahir antaḥ parāvaram
jnānaṁ jneyaṁ vaco vācyaṁ
tamo jyotis tv ayaṁ svayam
TRANSLATION
He who exists internally and externally, at the beginning and end of everything and of all living beings, as that which is enjoyable and as the enjoyer of everything, superior and inferior, is the Supreme Truth. He always exists as knowledge and the object of knowledge, as expression and the object of understanding, as darkness and as light. Thus He, the Supreme Lord, is everything.
PURPORT
Here the Vedic aphorism sarvaṁ khalv idaṁ brahma is explained. It is also explained in the catuḥ-ślokī Bhāgavatam. Aham evāsam evāgre. The Supreme Lord existed in the beginning, He exists after the creation and maintains everything, and after destruction everything merges in Him, as stated in Bhagavad-gītā (prakṛtiṁ yānti māmikām). Thus the Supreme Lord is actually everything. In the conditioned state, we are bewildered in our understanding, but in the perfect stage of liberation we can understand that Kṛṣṇa is the cause of everything.
īśvaraḥ paramaḥ kṛṣṇaḥ
sac-cid-ānanda-vigrahaḥ
anādir ādir govindaḥ
sarva-kāraṇa-kāraṇam
“Kṛṣṇa, who is known as Govinda, is the supreme controller. He has an eternal, blissful, spiritual body. He is the origin of all. He has no other origin, for He is the prime cause of all causes.” (Brahma-saṁhitā 5.1) This is the perfection of knowledge.