Bhagavad Gita 10.20 is Chapter 10, Verse 20, in Vibhuti Yoga (Divine Manifestations). Below are the Sanskrit text, a transliteration, a plain-English translation and an explanation.
aham ātmā guḍākeśa sarva-bhūtāśaya-sthitaḥ aham ādiś ca madhyaṁ ca bhūtānām anta eva ca
"I am the Self, O Arjuna, dwelling in the heart of all beings. I am the beginning, middle, and end of all beings."
What This Means:
The foundational vibhuti: Krishna is the SELF (atma) in all beings, not just externally present but intimately indwelling. And He's the beginning, middle, and end of all existence.
Going Deeper:
This is primary because it's universal. Every being has Krishna as their innermost Self. Before listing external manifestations, Krishna establishes His internal presence in everything.
How To Apply This:
The Divine isn't far, it's the deepest part of you. Before looking outward for manifestations, recognize the one dwelling in your own heart. The search begins within.
Key Sanskrit Terms: