January 2, 2025 , Genesis 4:1–7:24
We sometimes get caught up in unknowable details (often because we can express our opinions without much reproach) and miss the big picture. God put a mark on Cain. What's the mark? we want to know. Then we express our varied opinions. But the big picture is that God continued to care for Cain. Just so, when we sin, even horribly like Cain, God cares for us. Note further, that God's thanks for this is that Cain went away from his presence.
Though created in God's image, humankind continues to drift from the presence of the Lord. Due to the Fall, corruption increases on the earth. Part of this corruption is lording power over others. Let's call it bullying on a large scale. The Nephilim — again, despite our opinions — according to this verse, were physically mighty men, fighters, thugs.
All this and still more corruption leads to the Flood, God's initial attempt to reboot the earth. So, he saved one righteous man and his family, destroying the rest of the world. Note that the gospel flood is baptism and that all are saved who pass through that cleansing flood.