The flood came because of humanity’s persistent and pervasive wickedness. Yet even in judgment, God showed mercy by saving Noah, revealing both His righteous judgment and mercy.
The flood came because humanity’s corruption was so persistent and pervasive that “every intention of the thoughts of his heart was only evil continually” (Genesis 6:5), grieving God and demanding judgment. In response to the world’s rebellion, God responded with judgment but also showed mercy by preserving Noah, a man who walked with Him when no one else would. Jesus later used Noah’s generation as a warning of judgment that He will bring and a call to live righteous lives. Peter explains that the flood demonstrates God’s ability to judge the wicked while rescuing the righteous, previewing the final judgment to come. The flood also serves as a picture of salvation, pointing forward to Christ who brings us safely through judgment by His sacrifice for all who trust in Him. God grieves evil, confronts sin with justice, yet also extends mercy to those who trust Him.
We know that the world was absolutely corrupt, and though Genesis 6:6 says God "regretted" making humans, the direct translation of the Hebrew nahem is "grieved." God grieved the state of affairs. He desired, and always has desired, a right relationship with people. The people at that time were so evil, so in rebellion against God and His decrees, that God lamented, then decided to take radical action.
Remember, God is loving and merciful, but He is also holy and just. People continually sinned against Him, so He responded with resolve to act justly but also salvage the race of humans. Genesis 6:8 tells us that Noah found favor in God's eyes; verse 9 describes him as "a righteous man, blameless in his generation. Noah walked with God." God chose Noah and his family to be saved but assigned them the task of spending 120 years telling others about the coming destruction while preparing the ark.
Additionally, Genesis 6:2 tells us that "the sons of God saw that the daughters of man were attractive. And they took as their wives any they chose." This displeased God as well. In Hebrew, these "sons of god" are "bene elohim," a term most often used to describe angels (Job 1:6). Genesis 6:4 tells us that the offspring of these beings with human women were Nephilim. This word literally means "fall" but is often translated "giants." Some theologians say one strong reason for the flood was that God would not allow these creatures to continue to live. All of them, as well as the descendants of Cain, were wiped out in the flood.
All people today are descendants of Noah and his family. Noah was a descendant of Seth. Noah is listed in the genealogy of Jesus Christ, the vital and sole conduit for people to come into a right relationship with God.