
The Jews sin with the golden calf and God tells Moshe that he should leave Him alone so He can destroy the Jewish people. Moshe then prays that God should save the Jewish people for two reasons - one because of how terrible it would look to the world that God redeemed the Jews from Egypt and then destroyed them and also in the merit of our forefathers.
How do we understand this notion of Moshe praying that God should save the Jews in the merit of our forefathers? Wasn't Moshe the greatest person who ever lived? What merit did he not have which he thought could be found in our forefathers?
We must wask another question regarding Moshe's prayer. Later in the Torah in Parshas Shlach, God, once again wants to destroy the Jewish people and Moshe, once again, prays. But there, Moshe only mentions the first argument - that it will look bad to the nations of the world. Why didn't Moshe also mention the merit of our forefathers in that scenario?
Rav Soloveitchik explained that this was actually a major moment in Moshe's life where a major transformation occurred. Let us contrast the experiences of Avraham Avinu and Moshe Rabbeinu. Avraham finds God on his own and preaches monotheism to the world for decades before God ever appeared to him. He received no miracles and was challenged by God one time after another. Moshe, however, had it easy. God appeared to him, gave him signs to prove that he had God with him, and performed supernatural miracles in Egypt and the desert for him. Moshe, essentially, had to sacrifice little or nothing, while for Avraham and the forefathers, they had to sacrifice everything.
This is why Moshe prayed in the merit of the forefathers who up until that point were, in fact, greater than he. However, at this moment, Moshe rose to the occasion and told God that if He was not going to save the Jewish people, then he wanted no part of leadership and no mention in the Torah. Moshe, through this declaration, demonstrated that he was willing to sacrifice for God and the Jewish people. He was willing to lead a stubborn and difficult nation which would surely lead him to years of struggle and challenges. At that moment, Moshe rose beyond the level of the forefathers, explaining why he prayed in their merit after this sin, but not after the sin of the spies.
Those who choose the easy and lazy way out in life, lose out on the chance to strive for greatness. All of us have communities and families who need us to rise to the occasion and embrace a life of challenges and sacrificing for the Jewish people and Torah. Upon doing so, we, like Moshe, will also be catapulted to greatness.