Genesis 6 lays gives the background of the world at the time leading up to Noah and the Great Flood. In order to understand why God sent the Flood, it is important to consider the circumstances that preceded it – including the actions of mankind and the actions of God.
“And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.” (Genesis 6:5, emphasis added)
Mankind’s depravity had reached a level that evil entirely permeated every part of his being. His wickedness was great- that is, his actions were wicked. Every imagination was evil - his mind was wholly corrupted. Every thought of his heart – his will, his desires, his emotions, his passions, had all become so sin stained that there remained nothing within them that was not evil. These people upon whom God poured out the Flood were not merely dabbling in sin here and there, everything that they were doing was an horrific abomination!
“The earth also was corrupt before God, and the earth was filled with violence. And God looked upon the earth, and, behold, it was corrupt; for all flesh had corrupted his way upon the earth. And God said unto Noah, The end of all flesh is come before me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.” (Genesis 6:11-13, emphasis added)
Lest we have any doubts, let me say that the Earth was corrupted and filled with violence! There is a linguistic device employed in Hebrew that we see throughout the Old Testament, and that is emphasis through repetition. Whenever a word or phrased is used repetitively, it indicates a stronger or greater degree of the expression. The evil depths that the people who lived before the Flood had sunk to is strongly emphasized and amplified here in verses 5, and 11-13.
In considering why God sent the Flood, we must first realize that those living upon the Earth were completely and utterly wicked beyond the hope of changing. There were no innocent bystanders caught up in the Flood; everyone was guilty of the most deplorable sinfulness. The rebellion against God that we saw taking root in Cain and his descendants had now reached a fruition that God could not overlook.