Whereby. — The meaning of this is much disputed. The original literally signifies, by means of which things. But what things? The context allows various alternatives: (1) These facts about the Creation; (2) the heavens and the earth; (3) the water out of which, and the water by means of which, the world was made; (4) any or all of these together with the word of God. There is good reason for preferring the second of these. Both the heavens and the earth contributed to the deluge; for then “all the fountains of the great deep were broken up, and the windows of heaven were opened” (Genesis 7:11). The English “whereby” is as vague as the original.
The world that then was,... perished. — So that it is absurd to say that all things continue unchanged since the Creation. The world was so transformed by the deluge that the world previous to that catastrophe perished, chaos for the moment returned, and a new world issued from the crisis. “The world that then was, perished” is equivalent to “He spared not the old world” in 2 Peter 2:5.