Genesis 6:13

And the Lord said to Noah, The end of all flesh cometh before Me, because the earth is filled with rapine by their evil works; and, behold, I will destroy them with the earth.

VIOLENCE, that is, robbery and oppression. Now G-d gave Noah the explanation [that the flood was due to the fact that the “the earth is filled with] violence” and did not mention “the corruption of the way” [recorded in the preceding verse] because violence is a sin that is known and widely publicized. Our Rabbis have said that it was on account of the sin of violence that their fate was sealed. The reason for it is that the prohibition against violence is a rational commandment, there being no need for a prophet to admonish them against it. Besides, it is evil committed against both heaven and mankind. Thus He informed Noah of the sin for which the end is come — the doom is reached.

AND BEHOLD, I WILL DESTROY THEM ‘ETH’ THE EARTH. This is similar to saying “from the earth.” So also: When I go forth ‘eth’ the city, [meaning “from the city”]; he suffered ‘eth’ his feet, [meaning “from his feet”]. Another interpretation is that eth ha’aretz means “with the earth” for even the land was blotted out to the depth of a furrow of three handbreadths. Thus the language of Rashi quoting Bereshith Rabbah.
And Rabbi Abraham ibn Ezra said that the word mashchitham (destroy them) draws along with it a similar word, [meaning it is as if the verb “destroy” appears twice in the verse], thus stating, “And behold, I will destroy them and destroy the earth.”
By way of the truth [the mystic teaching of the Cabala], this is like the verse, eth hashamayim ve’eth ha’aretz (the heaven and the earth), thus intimating that “the earth” will be destroyed, and with the destruction of the earth they too will be destroyed and thus they will be blotted out from the World to Come, just as is intimated in the verse: and it grieved Him at His heart. It is to this that the Rabbis alluded in Bereshith Rabbah: “This is like a master’s son who had a wet-nurse; whenever he would commit an offense the wet-nurse would be punished.”

ויאמר..קץ כל בשר, a reference to the end of the period G’d had allocated to man for his repentance.

בא לפני, this period has now expired.

כי מלאה הארץ חמס מפניהם, for they all rob each other. The owners rob their leaseholders, the leaseholders rob the owners through deceit, so that in the final analysis all of the earth’s produce is grown for the benefit of robbers.

והנני משחיתם את הארץ, so that now I will destroy them together with the earth. I will destroy the climate which could support life on earth by interfering with the sun’s orbit and rearranging it from the beginning of the deluge for the entire future. We find that G’d explained this to Job In Job 38, 4-15. This accounts for the lifespan of man having been drastically reduced after the deluge. The climate of the earth changed, there were greater extremes of heat and cold, the produce of the earth was considerably less capable of supporting a long lifespan. As a by-product of this deterioration in the quality of the vegetable products, man was allowed to eat meat as a compensation.

ויאמר...קץ כל בשר, the time had arrived for their destruction from the world. The destruction which G’d had threatened before allowing for the 120 years grace period. Not only had they not mended their ways, but they had become ever more corrupt.

בא לפני, we have explained the word בא already elsewhere as meaning “that the time had arrived before Me.” The same expression is used in Jonah 1,2 when G’d describes the impending fate of the people of Nineveh in the words כי עלתה רעתם לפני, meaning that the effect of the wickedness had reached Him. The קץ described in our verse is the natural reaction to the effect the wickedness of the people had on G’d when it confronted Him.

כי מלאה הארץ חמס, the word מפניהם belongs next to the words בא לפני, i.e. on account of the violence they have perpetrated. Our sages (Sanhedrin 108) say behold how powerful is the sin of violence seeing that the generation of the deluge was not wiped out in spite of all their other sins until they had become guilty of indiscriminate violence. Iit was only then that the decree of their destruction was sealed.

משחיתם, seeing that the people had deliberately corrupted their way of life, G’d matches the punishment to the crime by depriving them of the control they used to exert over nature inasmuch as it effected their habitat, earth.

את, in this instance it means the same as מן, “from.” A parallel verse in which the word את is used in this sense is Exodus 9,29 כצאתי את העיר, “as soon as I leave the city.” Another such example is found in Genesis 44,4 הם יצאו את העיר “they had just departed from the city.”