Peter has just said that the Lord is patient with sinners, not rushing to judge the wicked – giving them time to repent (2 Peter 3:8-9).  Then comes, ‘But…’.  The ‘Day of the Lord’, that is the return of Christ as judge, is a fixed event in Father God’s diary (Matthew 24:36).  It will definitely happen, but there will be no more warning than if a thief visits your house.  Peter repeats what Jesus Himself said in Matthew 24:43 "But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into."

This statement divides the world into two groups, those who are waiting and ready to meet Jesus, and those who are neither expecting Him nor prepared to meet Him.  The unprepared group are in for more than a shock.  Not only will Jesus visibly and audibly appear (1 Thessalonians 4:13-18;  1 Thessalonians 5:1-3), all of a sudden with no immediate warning, but that event will start a process in which the planetary and stellar bodies in space will disintegrate spectacularly, and the earth itself will be a blazing inferno (2 Peter 3:7).

There will be no hiding place. Everything will be opened-up for Divine inspection and judgement (Hebrews 4:13), but those who love the Lord Jesus will be caught up with Him and saved (Daniel 12:2).  The repetition of the word "will" is significant to Peter.  It does not just imply a future tense, but it is God’s promise.  Peter is as certain about this cataclysm as about anything he has ever seen.  He does not say, ‘may’ or ‘could’ or ‘might’, because all those words give room for thinking that there is a chance that this great end-of-history event will not happen.  Peter would disagree; Jesus will definitely return to save His people and destroy the universe as we know it, before He creates a new heaven and new earth which will be the home of righteousness (2 Peter 3:13).

If your heart says, ‘I long for that day’, it shows how much you love the Lord, and are confident that the blood of Jesus will cover your sin, and ensure your welcome into God’s presence.  If you say, ‘I do not want that day to come’, it shows that you need to get right with God now, before it is too late (see www.crosscheck.org.uk).  Why are we told in advance?  So that we might all get ready (2 Peter 3:11), and help our friends and family to get ready as we share the gospel with them, and pray that they will repent and put their trust in Jesus.