The Torah tells us that when G-d had informed Avraham, our Patriarch, that He was going to obliterate Sodom, he immediately engaged G-d in a dialogue on their behalf. After the sin of the Golden Calf, G-d told Moshe that He was going to destroy the Jewish people and establish a new nation from him. Moshe, prayed to G-d that they should be forgiven. In contrast, when G-d informed Noach that He was going to bring an end to all existence because the world had become corrupt, Noach remained silent and did not respond.
Ohr HaChaim HaKadosh asks, “How could Noach, being of such dimension of righteousness, not seek mercy on behalf of his generation? When G-d had told Noach of the impending destruction of existence, it was clear the He had already reached the verdict that the world would be destroyed. There was no possibility that G-d would retract His decision. As it states, ‘The end of all flesh has come before Me...’ Noach understood from G-d’s terminology that it was a closed subject. It would be an affront to G-d if Noach would plead on behalf of his generation. However, when G-d communicated to Avraham and Moshe, He did so in a manner that indicated that His decision was not necessarily final. Thus, Avraham and Moshe were given the opportunity to plead for G-d’s Mercy.”
