Why did God destroy the pre-flood human race?
The pre-flood race became so wicked and rebellious that God had no remedy but to destroy them. Before the Flood, God dealt with one race based on conscience and blood sacrifice by faith, without organized worship, temple, or written law, yet the race fell apart.
Les teaches that from Adam until the Flood was approximately 600 years. From Adam until Abraham, God dealt with one race of people. In that period there was no organized system of worship, no temple, and no written law; it was simply based on man's conscience that if they knew they had sinned, they were to bring a blood sacrifice by faith. If their faith was real, their faith saved them, just like it does today. But because there was no organized law or worship, the human race fell apart until it got so wicked and so rebellious that God had no remedy but to destroy them. After the Flood, with Noah and his three sons Ham, Shem, and Japheth, the human race begins to split into three races.