Why was it necessary for Hashem Himself to judge the generation of Noach?
(6,13) “And G-d said to Noach: The end of all flesh has come before Me, for the earth has become full of robbery (חמס) because of them, and behold, I will destroy them from the earth.”
We can explain what the expression “has come before Me” comes to teach according to the Midrash which explains that the difference between a thief (גזלן) and one who takes by force (חמסן) is that the thief takes at least the value of a perutah (a small coin), whereas the other takes less than the value of a perutah. And it is taught in several places that a Beis Din does not involve itself in a case which concerns less than the value of a perutah.
According to this, this is the explanation of the posuk: “The end of all flesh”, that is, their end, “has come before Me” - I Myself will judge them. But why did it come before Hashem and not before Beis Din? The posuk answers this by saying “for the world has become full of robbery (חמס) because of them” - they are taking less than the value of a perutah, and so Beis Din is unable to involve itself. Therefore, Hashem needed to judge them Himself.
Why was the decree against that generation sealed only because of robbery?
(6,13) “And G-d said to Noach: The end of all flesh has come before Me, for the earth has become full of robbery because of them, and behold, I will destroy them from the earth.”
Rashi explains that the decree to destroy them was sealed only because of their robbery. Many commentaries have questioned why this was so.
But the Midrash explains that the generation of the flood were stealing less than the value of a perutah, and Beis Din does not involve itself in a case that concerns less than the value of a perutah. However, once they are already judging a case they can judge everything.
Thus, when Rashi says that their decree was sealed only because of their robbery, he means that their sin of robbery was not able to be judged except at the conclusion of their judgement. Because initially Beis Din was not able to judge them for the robbery since it was less than the value of a perutah.
How do we see in this posuk that the building of the Tower of Bavel was extraordinarily successful?
(11,3) “And they said to one another: Come, let us make bricks and fire them thoroughly. And the brick was to them for stone, and the clay was to them for mortar.”
The Yalkut comments that had extraordinary success in their building work - when they came to build one brick they instead built two. Where does the Midrash see an allusion to this in the posuk?
The answer we can learn from the gemora in Bava Basra 2a, which teaches that if two neighbours who jointly own a courtyard want to make a dividing wall in the middle, they have to build it according to the custom of the place where they live. If the custom is to build with stones, then each one must give three handbreadths of space, and if the custom is to use bricks they must give one and a half handbreadths of space.
From this we see that a stone is twice as large as a brick, yet here it says that "the brick was to them for stone", which is problematic since a stone requires twice as much space as a brick. Because of this the Yalkut explains that their work was blessed and a brick occupied the same space as if a stone had been placed there.