BBC: Genesis 7:17-24
The flood continued forty days on the earth. The waters increased and bore up the ark, and it rose high above the earth. The waters prevailed and increased greatly on the earth, and the ark floated on the face of the waters. And the waters prevailed so mightily on the earth that all the high mountains under the whole heaven were covered. The waters prevailed above the mountains, covering them fifteen cubits deep. And all flesh died that moved on the earth, birds, livestock, beasts, all swarming creatures that swarm on the earth, and all mankind. Everything on the dry land in whose nostrils was the breath of life died. He blotted out every living thing that was on the face of the ground, man and animals and creeping things and birds of the heavens. They were blotted out from the earth. Only Noah was left, and those who were with him in the ark. And the waters prevailed on the earth 150 days. – Genesis 7:17-24
The conclusion to this chapter establishes the practice of Biblical purification. The number forty, though having no special quality itself, is used throughout the Scriptures to refer to the full period of purification for God’s work. Moses and the people of Israel will encounter these periods throughout their history (Exo 16:35; 24:18; etc.).
The period of description is both full and encompassing. There is no place to hide from the purification of God. No flesh was able to hide from the sight of God in this judgment. The fullness of this “blotting out” can be against David’s sin (Psa 51:1) while still retaining a practical example. The complete removal of defilement is the goal of the Lord’s purification.
Both Paul (1 Cor 3:12-15) and Peter (2 Pet 3:6-13) describe similar events at the salvation of believers. The whole of creation will be purified as in the days of Noah. And the righteous will inherit the world like Noah.