Flood: Judgment for sin (Genesis 6 – 10)
Over the next several hundred years, as man multiplies in numbers, so his tendency to sin multiplies, until a time comes when God can find only eight people who are willing to live in a righteous relationship with Him: Noah, his wife, his three sons, and their wives. So, in judgment for sin, God performs surgery on the human race, cutting out the cancerous tissue, as it were, and leaving behind the healthy tissue to restore itself. He does this by sending a worldwide flood which destroys mankind, except for Noah and his family, who are saved in Noah’s ark.
Taken from 30 Days to Understand the Bible by Max Anders.