While this is an intriguing question I am not sure that there is a definitive answer. Why? Because both Abraham and Moses were absolutely integral to the Jewish Nation and it is inconceivable to imagine the Jewish People without either one of them.
Abraham was the founding father of the Jewish People – he is the first of the three forefathers and he is the very foundation of not just Judaism but all ethical Monotheism in general. He was a trailblazer and went against the grain in an idol-worshiping world. Abraham stood up against the powers of his time and started to preach the concept of Monotheism to anyone who would listen. He laid down the basis of Judaism and he successfully taught his son Isaac to withstand the social mores and to concentrate on delving deeper and deeper into his relationship with God. By doing so Abraham was able to instill in Isaac, Jacob and the generations that came after him the most fundamental concept of all – that there is a God and that our task as Abraham’s descendants is to do God’s bidding in this world.
Moses, on the other hand, did not have to establish Monotheism or to build a nation around him – they already existed. Moses’ task was to draw the Torah down into the physical world and, simultaneously, draw the Jewish Nation up towards the spiritual realms. Moses’ task was to teach the Torah to the Jewish People in such a way that they would understand it clearly and be able to implement it – even when Moses and the generation that heard the Torah from him were no longer around.
Perhaps the difference between the two can be seen through the titles that they are awarded and, by understanding what they mean, we will be able to understand clearly that they fill very different positions within the Jewish Nation and that they are equally indispensable. Abraham is called “Avinu” – our father. Moses is called “Rabbeinu” – our teacher. Abraham is our founding father, the one who gives us life and establishes our identity. Moses is the teacher, par excellence, who transmits the Torah to all the future generations and teaches us how to build a personal relationship with God. The same God that Abraham introduced to the world.
