The Thessalonian letters address the same issues as chapter 3. Scoffers at the Church has taken notice that the church has been saying (at the time of 2 Peter's writing) for 75 years that Jesus is coming back soon. After 75 years (which would seem a long time rather than soon from a human perspective) it would seem that perhaps he is not coming (see 3&4). The author's response is that the concept of "soon" and "time" are irrelevant to the Eternal One. One day is a thousand years and a thousand years are as a day. I am going to preach on 9/2 about what follows here -- the Lord is not wanting any to perish but all to come to repentance (9). I believe that. It is not God's will or intent that any human being should die outside of the purpose for which we were created. It is not God's will that any of us should live or die outside of God's love and grace and mercy and life! The implication, and an obvious one, is that, even so, some do. In 2 Peter's understanding the reason for Jesus delayed return is to give more people time to come to know and follow Jesus.
The author then reminds us that the return of Christ will be sudden (like a thief) and when its over its over. He ends the letter with a reminder to keep the faith and to hang on to what you have come to believe.