"Whereby the world that then was, being overflowed with water, perished." (2 Peter 3:6)
In comparing the intensity and global extent of the coming judgment of sinful mankind, "in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up" (v. 10), to the intensity of the historic judgment of sinful man at the time of the Flood (the denial of which constitutes willful ignorance, v. 5), Peter uses extraordinary language. The word "overflowed" in today's verse translates the mighty Greek word katakluzo, from which we get our word "cataclysm."
In the Greek New Testament, this word is only used to refer to Noah's Flood (see Matthew 24:38-39; Luke 17:27; 2 Peter 2:5); other words were used for other, local floods (see Luke 6:48 and Revelation 12:15). Such a distinction is likewise borne out in the Old Testament. The Hebrew word for "flood" used over and over again in Genesis 6-11 is mabul (see also Psalm 29:10) and stands as qualitatively distinct from other lesser floods, both of water and figuratively of invading armies, or the Red Sea crossing.
As a matter of fact, God promised that Noah's Flood would be different from all other water floods (Genesis 9:11), in that it was a display of God's awful wrath on sinful mankind and the world infected by that sin.
And that is the point. "The wages of sin is death" (Romans 6:23). It always has been, always will be. God is not the sort of God who will allow sin to go unpunished. His holy nature demands the punishment of death for sin.
But just as "Noah found grace in the eyes of the LORD" (Genesis 6:8), so do believers of today. The penalty for sin is indeed death, but "the gift of God is eternal life through Jesus Christ our Lord" (Romans 6:23). JDM