Genesis 7:18 Meaning

16And they that went in, went in male and female of all flesh, as God had commanded him: and the LORD shut him in.

17And the flood was forty days upon the earth; and the waters increased, and bare up the ark, and it was lift up above the earth.

18And the waters prevailed, and were increased greatly upon the earth; and the ark went upon the face of the waters.

19And the waters prevailed exceedingly upon the earth; and all the high hills, that were under the whole heaven, were covered.

20Fifteen cubits upward did the waters prevail; and the mountains were covered.