The enemy of our souls will use any means to attack us. The first attack here is against the Lord's own promise and the validity of the Scriptures, such as John 14:3 and Revelation 22:7, 12, 20. The scoffers were questioning why the Christians were still waiting for the Lord to come back for them (v. 4)!
A scoffer can still be saved. Compare the thief on the cross, who first mocked the Lord but then turned to Him for salvation.
Those who talk this way ignore the evidence of God's judgment. We have that evidence all around, including the world's numerous languages, which were God's judgment on man's pride in Genesis 11. The evidence given by Peter here is that of the Flood in Noah's time (Genesis 6).
These mockers were apparently religious. They knew the claim of Jesus' promised return, they knew about the fathers, and they knew about creation. But there was no reality in their hearts, and therefore they became mockers. Religion without a relationship with God will produce scorn for His truth.
Notice that the scriptures are sufficient to answer these mockings. At issue was the Lord's return, but the answer comes from God's interruption of human history in the Flood. The God who stepped into time in the past can certainly step into time again, which is what Jesus promised.
Believers were kept in 1 Peter 1:5. Here, the sinful world is kept (v. 7). There is no uncertainty of action with God.
The assurance of coming judgment gives us confidence in His justice. It should also motivate our activity in announcing the time of His patience.
Further, His longsuffering is toward "you" (some translations read "us"). His longsuffering is also grace towards believers by allowing us an opportunity to display faithfulness to Him while we await the Lord's return.
God often waits and waits and waits before He acts. But when He acts, it is swift, decisive, and final. Compare the experience of Joseph, who endured 13 years of injustice after his dreams. Then in one day God made him second-in-command over all of Egypt.
Another lesson is that we should be careful not to take the place of scoffers ourselves. We do this in practice by not responding in our hearts to the truth of His coming. Do we keep His coming before us so that it affects our daily walk?
Since God's judgment will be final on everything in this life (not only possessions, but on everything that might even remotely be our legacy), what should we do? There are some things that are eternal, and we can spend our days connecting our lives with them.
As far as gospel preaching is concerned, the Lord is still not giving up on anyone as of this date and this moment. Let's continue on for Him.