There were giants in the earth in those days. Genesis 6:4. The first people upon the earth received their instructions from that infinite God who created the world. Those who received their knowledge direct from infinite wisdom were not deficient
The Wicked Prepare to Attack the New Jerusalem
Satan … shall go out to deceive the nations … to gather them together to battle. Revelation 20:7, 8. In that vast throng are multitudes of the long-lived race that existed before the Flood; men of lofty stature and giant