Genesis 6 tells the story of a global flood in the days of Noah. TalkOrigins.org (an anti-Christian website) has graced us by providing a fairly thorough list of flood stories from around the world. This was a real event. But the reason it happened was that God saw how wicked man became, and God repented of making mankind:

Gen 6:5 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.
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.

Just so that the reader cannot misinterpret what is being communicated, the text then reinforces this concept with a quote from God:

Gen 6:7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.

The situation is as follows:

God made man on earth (for a love relationship).
Mankind flourishes (Gen 6:1).
Mankind becomes so evil that it “repents” God (literally like a deep exasperated sigh, as someone regretting something).
Then God decides to kill everything “both man, and beast, and the creeping thing, and the fowls of the air”.

Genesis 6 is describing a global reset. God regretted that He made man (this means if He were to do it again He would not have), and then God shows how serious He is about his regret (God undoes the thing He regrets doing). God destroys all living things!

This passage is not conducive to Calvinism. It shows deep, prolonged emotion in God based on seeing current events unfold. It shows God reacting to His knowledge in real time. If God had known man would become this wicked, there would not be a regret in God. Why would God do something He knows He would regret? Before creation, He was not even being persuaded by a third party (as when Moses convinced God to spare Israel). The wickedness would be part of God’s plan or it would not faze God. But the text reveals a deep hurt in God, emphasized by drastic action.

Because God is righteous He spares one family because of the righteousness of one man (the text never calls Noah’s sons righteous). After the global reset, God has another change of heart. He had destroyed the world because it was evil but then resolves to allow the world to be evil because people are naturally evil:

Gen 8:21 And the LORD smelled a sweet savour; and the LORD said in his heart, I will not again curse the ground any more for man’s sake; for the imagination of man’s heart is evil from his youth; neither will I again smite any more every thing living, as I have done.

God destroyed the world because the “wickedness of man was great in the earth”, but afterwards decides to never again destroy it “for man’s sake” because “the imagination of man’s heart is evil from his youth”. Some atheists call this a contradiction. I call it giving up hope in humanity. This directly results in God trying to then work though individuals instead of humanity in general.