I find it more than remarkable that the "proof" God offers for Moses' authority is the worship the Hebrews will offer on Mount Sinai. We usually look for more spectacular demonstrations and there are plenty in the history that follows this conversation in the wilderness. Who would not be persuaded by the ten plagues that afflicted the Egyptians, the parting of the Red Sea and the complete destruction of Pharaoh and his army? But these mighty deeds were not the proof the Lord offered. Nor would they prove a reliable foundation of faith.
Rather, it was the worship the Hebrews offered on "this very mountain."
"No sign will be given!" Jesus thundered at his critics. His changing water to wine and feeding five thousand in the desert did not satisfy them. Neither his compassionate healing nor his numinous presence could bring them round. They would not see his passion, death and resurrection as a proof of his authority. As he had prophesied, "If they will not listen to Moses and the prophets, neither will they be persuaded if someone should rise from the dead."
We read of that proof in Exodus 24, when Moses presided over the Mount Sinai covenant. He sprinkled the blood of an ox on the people and on the altar, which represented God. Thus they were bound together in the blood.
The Church sees this remarkable ceremony as a prototype of the Mass. We are joined to our God and to one another in the Blood which was shed on Mount Calvary. It flowed from his open chest when a soldier pierced his side with a lance; it is the very blood which we drink at the altar.
The proof God offered during that burning bush epiphany was the covenant of communion with himself. This sign is recognized with the eyes of faith, by those filled with the Holy Spirit.
There will always be cynics and critics who demand more persuasive, "scientific" proof. They point to the persistence of evil -- which abides even in Christian hearts! -- to show that an all-powerful God is neither good nor just.
Our eyes have been opened and we see God's vindication on Calvary and our Communion in the Blood of the Lamb.