Dora Bas Rivka Silver O'H
"Knock Knock." "Who's There?"
G-d appeared to Moshe and identified Himself by the Tetragrammaton (Y-H-V-H), which He said was a Name not made known to the Patriarchs. Of course, literally, the Forefathers knew and used this Name, as we see several places in Genesis. Rather, it means that the Patriarchs interacted with other aspects of G-d, as reflected by His other Names. (Rashi says that the Forefathers did not live to see the fulfillment of the promise G-d made using that attribute. In that sense they did not know Him by that Name.)
G-d told Moshe to assure the Jews that He has heard their suffering and that help is on the way. He will show His might to the Egyptians, after which the Jews will be His people exclusively. He will take them to the land He promised their ancestors. Moshe conveyed the message, but the people were so disenchanted after their previous disappointment that they didn't pay him any attention.
G-d told Moshe to return to Pharaoh; Moshe replied that Pharaoh had less reason to be responsive than the Jews did! G-d added Aharon to the loop and He gave the brothers instructions.