Chazal point out that Hashem is described differently to Moshe than He is to the Avot. To the Avot He is described as “Kel Shakai,” while to Moshe He is described as “Hashem.” However, there are some places where Hashem is described as “Hashem” to the Avot. Hashem first says in Bereishit 15:7, “I am Hashem who took you out of Ur Kasdim to give you this land as an inheritance.” Then, Hashem speaks to Yaakov in Bereishit 28:13 saying, “ I am Hashem, God of Avraham your father, God of Yitzchak. I will give you and your descendants the land upon which you lie.” Rashi explains these Pesukim by referring to a Pasuk in Shemot 6:3, where it is written, “I was not known to you my name Hashem.” Hashem does not say “I did not make known,” rather, He says “I was not known,” for His true nature was unknown to them. Hashem did say His name to the Avot, but they did not know its true meaning. According to Rashi, the meaning of “Hashem” is to fulfill promises, and when Hashem spoke to the Avot, He had not yet fulfilled His promises to them.
This poses another question. Why, during the time of the Avot, does Hashem not fully demonstrate His attributes to them? Was Moshe greater than the Avot? According to Chazal in Midrash Rabba of Shemot 6:4, not only was Moshe not greater than the Avot, but he was even rebuked for his lack of faith. According to the Kuzari (2:2), the fact that Moshe received greater revelation from Hashem had nothing to do with the greatness of Moshe’s generation, rather, it was because there were a great number of people who were doubtful of Hashem at the time. Therefore, a greater revelation was required. The Avot, though, were a small group of people with unbendable faith in Hashem, even throughout all the suffering during their lives. Therefore, such a great revelation was not necessary.