The concept of the return of Christ being like a thief in the night comes from 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.” The essential elements of Jesus’ warning are that no one knows when He will return, and we have to be in a state of preparedness, always watching for His imminent return. Jesus warned that we should always be prepared because no one except the Father knows the hour of His return (Matthew 24:36–44).
This event has become known as the Rapture. The word “rapture” appears nowhere in the Bible, but the event does. The word used in the Greek is harpazo (“to catch away; to snatch”), found in 1 Thessalonians 4:16–17: “For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever.”
The sudden nature of this event is described in 1 Corinthians 15:51–54 as “a flash, in the twinkling of an eye.” There will be no warning of Christ’s coming, just as a thief in the night comes without warning. Therefore, Matthew 24:44 tells us, we must “be ready, because the Son of Man will come at an hour when you do not expect him.”
For the Christian, the Rapture will be a welcome event, but for everyone else it will be a time of great tribulation. Imagine being left behind while millions of Christians all over the world suddenly vanish without explanation. We have been sufficiently warned by the Bible and the testimony of God’s own Son to be prepared. We must be vigilant, and we must be protected by the full armor of God (Ephesians 6:13–18). The devil roams the earth looking for Christians with a chink in their armor. Do not be fooled into believing the devil only focuses on sinners. He already owns them and has no reason to bother with them unless they begin to spiritually awaken to Christ Jesus. The devil’s concern is the Christian. We are the ones he wants to corrupt and destroy, and that is why Christians must be ever watchful and ready for the hour of our Lord’s return.
We also have the presence of God’s Holy Spirit to teach us and guide us. We have everything we need to live godly lives in obedience to God’s Word, leaving no excuse for being unprepared.
We thank God that He loves us enough to provide the way for us to escape and the judgment of God. That way is Jesus Christ. By accepting Jesus Christ as our Lord and Savior, and by the grace of God, we are granted forgiveness of sins, mercy and salvation with the promise of everlasting life (John 3:16; Ephesians 2:8–9). Our salvation in Christ is the means by which we may be prepared and rejoice in His return.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.