Commentary for Genesis 6:11

ותשחת [THE EARTH] WAS CORRUPT — It means lewdness and idolatry, as (Deuteronomy 4:16) פן תשחיתון “lest ye deal corruptly” (the following words show that this refers to idolatry) and as ‘כי השחית כל בשר וגו “for all flesh had corrupted etc.” (in next verse of this chapter where Rashi states that this has reference to lewdness) (Sanhedrin 57a).

ותשחת הארץ. The earth had become corrupt. This entire verse is superfluous in view of 6,5. If the Torah only wanted to spell out details of man's sins, this too had been spelled out in greater detail in the previous passage. If the Torah wanted to add the element of violence perpetrated by man on earth, that is all that needed mentioning here. Besides, why did the Torah switch to the use of the name אלוקים, the attribute of Justice, whereas in 6,5 G'd's attribute of Mercy is used? What do the words לפני האלוקים in our verse add to our understanding? Why does the Torah repeat once more in 6,12 that "G'd saw, etc.?" The Torah certainly did not need to tell us that G'd had become aware of man's sins, as we all know that He is aware of all this?

ותשחת הארץ, the people on earth had become corrupted; we have a similar formulation in Exodus 1,2 where the Torah writes of the Israelites ותמלא הארץ, and the meaning cannot be that the whole earth was filled with Israelites. There are many examples of similar stylistic formulations used in the Torah.