Question: How did Moses know that God Is God at the burning bush? G-d is beyond description, has no form and defies human classification. Why didn’t Moses ask for some identification?
Answer: I suspect that the answer is that the experience of direct contact with God is so unique that it does not require special proof. Further, later on, Moshe does demand methods by which to demonstrate that God has sent him – which God provides.
Rabbi Daniel Freitag