3 Above all, you must understand that in the last days scoffers will come, scoffing and following their own evil desires. 4 They will say, “Where is this ‘coming’ he promised? Ever since our ancestors died, everything goes on as it has since the beginning of creation.” 5 But they deliberately forget that long ago by God’s word the heavens came into being and the earth was formed out of water and by water. 6 By these waters also the world of that time was deluged and destroyed. 7 By the same word the present heavens and earth are reserved for fire, being kept for the day of judgment and destruction of the ungodly.
8 But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day. 9 The Lord is not slow in keeping his promise, as some understand slowness. Instead he is patient with you, not wanting anyone to perish, but everyone to come to repentance.
(2 Peter 3)
Basically, people in the last days (what "last days" he's talking about, I don't know) would start to question why Jesus isn't coming back considering that the apostles kept writing them letters, telling them to live their lives as if the return of Jesus was imminent, and this is what Peter has to say about this.
