2 Peter 3:3-7

³ knowing this first: that scoffers will come in the last days, walking according to their own lusts,

⁴ and saying, “Where is the promise of His coming? For since the fathers fell asleep, all things continue as they were from the beginning of creation.”

⁵ For this they willfully forget: that by the word of God the heavens were of old, and the earth standing out of water and in the water,

⁶ by which the world that then existed perished, being flooded with water.

⁷ But the heavens and the earth which are now preserved by the same word, are reserved for fire until the day of judgment and perdition of ungodly men.

scoffers (v.3) = lit. “scoffing scoffers,” mockers, false teachers

Led by the Spirit of God, Peter prophesies that in the last days scoffers will arise questioning the validity of Christ’s Second Coming to the earth. They will brazenly ask, “Where is the promise of His coming?” First, the “last days” here are the last days of Israel according to the Prophetic Scriptures (Joel 2:28-32 cf. Acts 2:14-18). Unlike the “last days” in Paul’s epistles, these days will be closely identified with signs (Matthew 24:30 cf. Acts 2:19-20), times (Matthew 24:15), and seasons (Matthew 24:20-21).

This is the time of Jacob’s Trouble that will cover a period of seven  years and be brought to a close by the Second Coming of Christ to execute judgment upon His enemies. In the early part of the Tribulation, scoffers will declare that they don’t see any of these things taking place, “for since the fathers fell asleep, all things continue as they were from the beginning of creation.” That, of course, is a blatant lie, which Peter was not about to allow to pass without a challenge. — Sadler, pages 222-223.

fathers (v.4) — Likely the patriarchs and prophets of Israel who predicted the Lord’s coming appearance and judgment—the “promise” that the scoffers said wasn’t coming.

Like many today, these scoffers are going to hold to the doctrine of Uniform-itarianism. According to this interpretation of earth history, existing physical processes, acting essentially at the present rates, are sufficient to account for all geological formations. In other words, every thing has remained the same or uniform since the beginning. …

[But] … the Word of God … says that there was a catastrophic event in Noah’s day known as the universal flood, which destroyed the earth (vs. 5-6). Clearly Peter believed and taught the universal judgment of the flood in the days  of Noah.

But what does Peter mean by “the earth standing out of the water and in the water”? On the second day of creation God separated the waters from the waters, which formed a protective vapor canopy around the earth (Genesis 1:6-8). Hence, we have “the earth standing out of the water.” … Second, the earth standing “in the water” is a reference to the subterranean waters just beneath the earth’s surface, which were apparently used to cool the earth’s crust after creation. …

After the fall of man, these two great bodies of water above and beneath the earth’s surface, once intended to be a blessing, were reserved as an instrument of judgment upon the ungodly deeds of men. At God’s appointed time, He broke up the fountains of the deep, which probably resulted in tidal waves sweeping across the face of the earth. Simultaneously, God opened the windows of heaven, allowing the vapor canopy to condense and gradually fall to the earth in the form of torrential rain that spanned forty days and forty nights (Genesis 7:11-12). … Every living thing that walked the earth, with the exception of the inhabitants of the ark, perished in a watery grave. Peter substantiates this when he says “Whereby the world that then was, being overflowed with water, perished” (v.6). So we are to understand that the present heavens and earth are vastly different than the old world that perished. …

Although the scoffers claim “all things continue as they were from the beginning of the creation,” according to the Word of God, this is just not the case. So the present is not the key to the past, as many have been led to believe. Rather, the present heavens and earth differ immensely from the old world that perished. — Sadler, pages 224-226.

I found this online:

More accurately, “and the earth formed out of water and by means of water.” The words carry us back to the cosmogony of Genesis 1. The earth was brought out of chaos into its present kosmos, by the water being gathered into one place and the dry land appearing (Genesis 1:9). It was kept together by the separation of the waters above the firmament from those that were below the firmament (Genesis 1:6).

And this:

The narrative in Genesis represents water as originally overspreading all things. “The earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.” We may therefore understand Peter as meaning that the earth was formed or compacted out of water, or out of those substances which the water at first held in solution; and that it is kept together in coherence and solidity by means of water.

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Why is it that these scoffers were so insistent that nothing had changed since the beginning of creation? So much so that they were willingly ignorant, as Peter says, regarding the global deluge in the days of Noah. You see, if they acknowledged that God judged the world as a result of evil in time past, then the probability that He will judge the wicked deeds of men in the future day of the Lord is even greater! While God has set a boundary that the waters will never again cover the earth, He will one day purge the present heavens and earth with fire (Psalm 104:5-9 cf. Matthew 3:7-12). — Sadler, page 226.

perdition (v.6) = destruction, ruin

Romans 1:20 says “For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse.” I’ve always thought of that exclusively in terms of God’s original creation on the six days, and that is certainly true. But the evidence of God’s judgment via the Flood is also unmistakable in creation. The very evidence that proves the earth was flooded—the layers, the fossil record, the appearance of sea creatures in fossils on mountain tops—is used by secular evolutionists to “prove” their ungodly theory. This is just another way they willfully refuse to glorify God and be thankful to Him (Romans 1:21 cf. 2 Peter 3:5 on “willfully forgetting”) As a result, although they think the sound wise, they become fools (Romans 1:22). I haven’t thought of the evidence of creation in quite this way before. The universal Flood is certainly evidence of God’s power.

So Peter is warning his readers to beware of the idiots who claim that God won’t judge the world when all around them is clear evidence that God has indeed judged the world and so can be trusted to keep His promise to do it again.