Arjuna touches on something subtle here. You know Yourself by Yourself. No external proof is needed. No outside authority can confirm what the divine already knows from within. Like a lamp that needs no second lamp to see its own light — the divine is self-illuminating.
Four addresses follow in quick succession: Bhootabhavana (creator of all beings), Bhootesha (Lord of all beings), Devadeva (God of the gods), Jagatpate (ruler of the world). Each widens the circle. He creates, He governs, He stands above even the gods, and He holds the entire cosmos.