Secular world-views can subtly infiltrated the way we as Christians view life, reality, and the future. It is very possible to be a conservative Bible believing Christian and yet have an outlook on life that is far more focused on the present than on eternity.
Christians back in the first century were being and today are still being influenced by the same attitude that assumes that tomorrow will be just like today. “Since nothing has changed, nothing ever will - so live for today.” This can be talking about either a good or a bad situation. A person can be either be complacent because things are going well for them right now or else, in a negative situation, believe that God will never bring judgment or justice at home, at work, or in their relationships.
That is why Peter is telling the church to remember that the Lord is not being slow about fulfilling his promise but is being patient for our sakes because he doesn’t want anyone to be destroyed. He was describing people that mock the truth and who deliberately forget that God made the heavens and earth by the word of His command, and that the heavens and earth are being kept for the day of judgment.
If you and I really considered how uncertain and short life is, and how little control we have over it, it would shape the way we live our lives each day. We can’t take tomorrow for granted. This understanding does not just apply to the limited number of days you as an individual have on this earth but to understanding that the days of the heavens and earth are also numbered. Peter wants his friends to understand that even though God is delaying His coming because of His patience towards us and the people around us, as Christians we need to be prepared for that day. Because on the day the Lord returns, it will come suddenly.
But the day of the Lord will come like a thief. The heavens will disappear with a roar; the elements will be destroyed by fire, and the earth and everything done in it will be laid bare. Since everything will be destroyed in this way, what kind of people ought you to be? You ought to live holy and godly lives as you look forward to the day of God and speed its coming. That day will bring about the destruction of the heavens by fire, and the elements will melt in the heat. But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells. (2 Peter 3:10-13)
What is the Day of the Lord?
The Day of the Lord is so unique and significant that it is also referred to as “that Day” in passages such as Isaiah 5:30, Zach 1:15, and Mark 14:25. As is often the case with Old Testament prophecy “that day” usually refers to a two-fold fulfillment, near and future events. In the New Testament, the Day of the Lord can refer to the entire period from when the initial judgments of God are first manifested (at a time of relative peace and safety) through the end of the Millennium (in the broad sense). Andreas Kostenberger writes:
Every day we come across people in our workplaces, at school, at the gym, and at events, who scoff at and mock the Bible, deny God’s existence, and live self-absorbed lives. Even many Christians who believe in God live as though God has nothing to do with their daily lives. We hear about acts of senseless evil, people calling good evil and evil good, and it really does seem, at times, that God has turned a blind eye to all these things. We may ask, “Why doesn’t God bring judgment on all the evil that takes place around us?”
But the day designated in the Bible as the “Day of the Lord” is coming and when it comes it will be abrupt. One thing we can be sure of is that God will bring every person into judgment in His way and in His timing. God will punish all sin and evil with wrath and judgment and will judge those who have rejected Christ. So what will the day of the Lord be like? 
For the Unbeliever:
Will be a surprise
Will be severe
Will be sorrowful
For the Believer:
Will come suddenly not surprisingly,
Will be sanctifying
Will be a day of salvation and celebration
The Scriptures tell us in verse 10, that the Lord will come like a thief. He will come when no one is expecting Him. For the unbeliever...
It will be a surprise
…and sudden for those who were living as though God didn’t exist or one’s belief in God didn’t matter. Jesus explained what “that Day” will be like in Matt 24:37-39:
When the Son of Man returns, it will be like it was in Noah’s day. In those days before the flood, the people were enjoying banquets and parties and weddings right up to the time Noah entered his boat. People didn’t realize what was going to happen until the flood came and swept them all away. That is the way it will be when the Son of Man comes (Matthew 24:37-39 NLT).
These people ignored Noah that righteous preacher who was building an ark in front of their eyes for 120 years. No different today, the Day of the Lord will come when the world is expecting peace and safety for the present. This is what they seek but they do not have any peace for their eternal future. Paul wrote:
For you know quite well that the day of the Lord’s return will come unexpectedly, like a thief in the night. When people are saying, “Everything is peaceful and secure, then disaster will fall on them as suddenly as a pregnant woman’s labor pains begin. And there will be no escape (1 Thessalonian 5:2-3).
It will be severe
The heavens will disappear with a roar; the elements will be destroyed by fire. The heavenly bodies and the earth will be changed.
The Day of the Lord is a Day of Calamity. The day of the Lord means destruction for the godless. The prophets excel in describing the calamitous aspect of day of the Lord. Amos speaks of it as a day of darkness (5:18). Joel depicts it as a day of clouds and thick darkness (2:2). Zephaniah's description (1:15-16) is vivid as he mixes direct description and metaphor:
That day will be a day of wrath,
A day of distress and anguish
A day of trouble and ruin,
A day of darkness and gloom,
A day of clouds and blackness
A day of trumpet and battle cry
It will be sorrowful
Revelations 1:7 says Behold, He is coming with the clouds, and every eye will see Him--even those who pierced Him. And all the tribes of the earth will mourn because of Him. So shall it be!
There will be shock, sadness, sorrow and shame. It will come without warning and take wicked people by surprise. Think about people who don’t know the Lord that are worth billions of Euros, own yachts and private jets. They own villas around the world and even own whole islands, have no material needs or wants, and wield unfathomable amounts of power and influence. On that Day, all that they know and everything they own will be gone in seconds. When Christ comes back, they will realize whom they have rejected and this will have eternal ramifications. When God judges each person it will be with righteous, perfect judgment.
These people have countless opportunities to humble themselves and turn to God. But on that Day, it will be too late and they will have no excuse. If they have rejected the truth they will suffer separation from God and be cast into hell for eternity. Hell will be a place of intense pain and suffering forever for all eternity. (Rev 21:8). That is why Peter says to remember that because of our Lord’s patience, He is given people time to repent and to be saved. God does not want any to be destroyed but desires that every person would choose to turn to Him and spend eternity in heaven with Him.
What will it be like for Christians on the Day of the Lord?
It will come suddenly but not surprisingly!
But you aren’t in the dark about these things, dear brothers and sisters, and you won’t be surprised when the day of the Lord comes like a thief (1 Thess 5:4).
Nobody, except God, knows the date or time that the Lord will return but as Christians, we know it is coming and are, therefore, to live in steadfast anticipation of that Day.
Peter asks a rhetorical question: Since you know that everything you see, all that you see will be destroyed (cease to exist) in this way, what kind of people ought you to be? How are you living for the Lord? In light of the imminent return of the Lord, Peter said that we should live holy and godly lives, looking forward to that Day. For the Christian that Day...
Will be sanctifying
People who question the reality of the Lord’s return, many times, could care less how they live because they don’t believe in the coming judgment. But God’s people are not only aware that the Lord is coming back but realize that the Day of the Lord will be a day of reckoning for them as believers (2 Cor 5:10). We will all appear before the judgment seat of Christ. This is when God will openly manifest everything about our lives. This is not a day of wrath nor of judgment with regards to our salvation because all of our sins were paid for by Jesus, but a day of judgment for how we lived as His son or daughter - for everything we did on this earth, whether good or bad.
Each person will be judged for the good - that which originates from God and is empowered by Him in his or her life, through faith. A person will be rewarded for the times he or she humbled themselves and trusted Him, times they walked in integrity, walked in obedience regardless of the circumstances.
He will also hold each person accountable for everything he or she had done with their bodies that was worthless. Each person will be judged for every worthless action, evil thought and every unprofitable and injurious word they spoke to and about other people (Matt 12:36). Can you imagine what that will be like? God is not going to sit there on His throne and say, “Oh, I understand why you made this or that decision. Why you were the way you were, did the things that you did.” On that Day, God is not going to reward us for a living a life of selfishness or self-preservation. There will be no pointing the finger at anyone else for the decisions we made.
Peter knew that each person in the church would stand before the Lord and so he was exhorting them to live virtuously in their lifestyle and habits (holy) and in their relationship to God (godly).
Paul told the church in Thessalonica, “Therefore let us not sleep, as do others; but let us watch and be sober” (1 Thess 5:6).
The word sober in the original Greek is defined exactly how it is in English. It is the word for not being intoxicated. We are so prone to being intoxicated and not necessarily by alcohol but with the stimulants of the world — its glamor, its appearance, and pursuits of the pain free life. In contrast, we need to be sober, watching and waiting!
J. Vernon McGee said:
That is why we talk about developing godly character in the sermons, in life groups, and in the youth connect group with the teenagers. As Christians, we shouldn’t have the attitude, “Oh I just can’t wait to get to heaven to be sanctified” - we have opportunities to live for God now, we do not have to wait till heaven.
And we should not only live a godly, holy life in the fear of the God but have compassion on those who do not know the Lord. We, who know that the Day of the Lord is coming and have our final destination secured, need to be pointing our friends and family members to Christ so they can be prepared for that Day. As a church, we need to ask God to give us compassion for the lost and make a plan to reach them. And lastly, For followers of Christ, the Day of the Lord...
Will be a day of salvation and celebration
For believers this Day means to be caught up to be with Christ, their Redeemer forever (1 Thess 4:13-5:3). “For God chose to save us through our Lord Jesus Christ, not to pour out his anger on us” (1 Thess 5:9 NLT). The Lord will change our mortal bodies to immortal, in the twinkling of an eye.
Christians can look forward to the Day of the Lord with great expectation and intensity. Knowing that He is coming again, we can encourage each another with great anticipation and joy because “we are looking forward to a new heaven and a new earth, where righteousness dwells” (vs. 13). Peter is quoting from the book of Isaiah:
Look! I am creating new heavens and a new earth, and no one will even think about the old ones anymore (Isa 65:17 NLT).
As surely as my new heavens and earth will remain, so will you always be my people, with a name that will never disappear,” says the LORD (Isa 66:22).
As we mentioned earlier, the Day of the Lord describes near and future events, it encompasses several eschatological events such as the second coming, the resurrection of the dead, and the final judgment. And once God has executed final judgment on all people and on heaven and earth, everything will be made new. The negative effect of sin which have corrupted all of nature, animate and inanimate and even to the heavens (or atmosphere) will be burned up, purified by fire. God will make a new heaven and earth, it shall be fresh and glorious, with no trace of the damage caused by sin, natural disasters, pollution or the ravages of human exploitation. No more death, disease, no more physical, or emotional pain.
One of the amazing realities of eternity is you will have no memory of the old. You will be living in the new heaven and the new earth and the things that have happened in the past, what it was like before, will not be remembered or come to mind. The heavens and earth will be of a new kind, unprecedented. The new heaven and earth is where righteousness dwells (Rev 21:1-6). God will take up His rightful position over the new residence and rule over and among His people (1 Pet 2:9). This is not meant to make light light of the sins that we struggle with, or the battles we fight here on earth each day. As painful as these things are we can turn to Jesus and remember they are just moments of distress in light of eternity.
On that Day Jesus will declare, “It is finished! I am the Alpha and the Omega—the Beginning and the End. To all who are thirsty I will give freely from the springs of the water of life” (Rev 21:6).
On that Day there will be nothing between my Savior and I, nothing to hinder me from receiving what I need to quench my thirst. This is what we have to look forward to on the Day of the Lord. My question is “How will you choose to live until then?