Peter was writing, at the time, against the theory of uniformitarianism. It states that the processes affecting Earth today are the same ones that affected it in the past. Looking forward, Peter writes of how skeptics will argue using ridicule and mockery. I like the GNB translation of verses 3-4…
“First of all, you must understand that in the last days some people will appear whose lives are controlled by their own lusts. They will make fun of you and will ask, “He promised to come, didn’t he? Where is he? Our ancestors have already died, but everything is still the same as it was since the creation of the world!””
2 Peter 3:3-4 GNB
“Everything is still the same as it was” indicates that they never really knew God to begin with. If they had, they would know the truth. Faithless people argue that since “nothing” has happened, God must not exist. This is why Peter follows up with the creation story and a reference to the flood. He’s trying to remind everyone not to be put to sleep by these false doctrines!
“But do not forget one thing, my dear friends! There is no difference in the Lord’s sight between one day and a thousand years; to him the two are the same. 9 The Lord is not slow to do what he has promised, as some think. Instead, he is patient with you, because he does not want anyone to be destroyed, but wants all to turn away from their sins.”
2 Peter 3:8-9 GNB
Those who mock Him have no idea that the extra time they are experiencing is for their own good – to see the truth and turn from their sin. Peter ends the chapter on a familiar note. He once again reminds us to remain faithful and not to tolerate false doctrine!