Musar zu Schemot 3:6

I have already alluded to the Midrash which describes Moses as a טירון, private, in G–d's army of prophets at the beginning of his career when he experienced his first vision of G–d at the Burning Bush. G–d had said to Himself at that time: "If I appear to him with a thunderous voice, I will frighten him. If I approach him in a low voice, he will treat prophecy with scorn. So what did G–d do? He addressed him using the voice of Moses' father Amram. When thus approached, Moses responded by saying: הנני, "I am ready" (what does my father wish of me?) (Exodus 3,5). G–d then told Moses that He was not his father but the G–d of his father, that He had called him in a seductive manner so as not to frighten him. He explained that He was also the G–d of Abraham, Isaac and Jacob. Thereupon Moses was very happy to hear that his own father was included in the list of patriarchs, and had even been mentioned ahead of the patriarchs. At this point, Moses hid his face, saying that he must surely hide his face in the presence of the G–d of his father.