The Bible is very clear why the Flood came:

 Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. And the LORD was sorry that He had made man on the earth, and He was grieved in His heart. So the LORD said, “I will destroy man whom I have created from the face of the earth, both man and beast, creeping thing and birds of the air, for I am sorry that I have made them.” (Genesis 6:5-7)

The Flood was sent as a worldwide punishment for people’s sins. The fact that people had sinned greatly is seen in the accounts of various lives at the end of Genesis. For example, Cain’s great-great-great-grandson, Lamech, took two wives for himself. Thus we have the beginning of polygamy, which so plagued various characters of the Old Testament — even God’s servants, such as David and Solomon. Lamech also boasted about his power:

“For I have killed a man for wounding me, even a young man for hurting me. If Cain shall be avenged sevenfold, then Lamech seventy-sevenfold.” (Genesis 4:23-24)

The difference was that it was God who promised vengeance on those who were to harm Cain. Lamech, five generations on, was promising his own retribution. He was putting himself in the place of God. He was claiming for himself the right to exact an unbalanced revenge, where his retaliation would far outweigh the supposed wrong he had suffered. The Bible is not clear whether this was an idle boast, or a real threat. I suspect the latter, however, since Lamech had remarked that he had killed a man younger, therefore perhaps supposedly fitter, than himself.

There are many different ideas about who the sons of God and daughters of men mentioned in Genesis 6 were. This is perhaps not the place to address this particular controversy1, except to note that there was careless, or carefree, marriage going on. Jesus reminded us that the days preceding His Second Coming would be similar.

“For as in the days before the flood, they were eating and drinking, marrying and giving in marriage, until the day that Noah entered the ark, and did not know until the flood came and took them all away, so also will the coming of the Son of Man be.” (Matthew 24:38-39)

Although the pre-Flood people did not know the exact day of the disaster that was to come, they were aware, or should have been aware, that it was coming, just as surely as Jesus will come again. God had already given them a 120-year warning:

 “My Spirit shall not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years.” (Genesis 6:3)

God has already warned our present generation that He will not always strive with mankind. There will be a reckoning — a Day of Judgment. The rest of Matthew 24 makes this clear. So why did God choose to save someone like Noah? Was it because he was a very good man?

No. It was because “Noah found grace in the eyes of the LORD” (Genesis 6:8). That is why the apostle Paul reminds us:

 For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast. (Ephesians 2:8,9)

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  1. My thoughts on the matter are contained in my book, The Six Days of Genesis, published by Master Books.