Matt 24:43-44 NASB
Jesus exhorts us to be alert and ready for His appearing. While it is true that we do not know the day or hour of His coming, this statement does not stand alone by itself. Jesus has just finished foretelling the signs and events leading up to His return, so we must take this passage as a whole. We have been given distinct things to watch for. His coming will be unexpected for many, but those who are awake and watching will be ready as they see the signs fulfilled.
Now as to the times and epochs, brethren, you have no need of anything to be written to you. For you yourselves know full well that the day of the Lord will come just like a thief in the night. While they are saying, "Peace and safety!" then destruction will come upon them suddenly like labor pains upon a woman with child, and they will not escape. But you, brethren, are not in darkness, that that day would overtake you like a thief; for you are all sons of light and sons of day. We are not if night nor of darkness; so then let us not sleep as others do, but let us be alert and sober.
1 Thessalonians 5:1-6 NASB
In a similar fashion Paul admonishes his readers to be on the alert as well. While the return of Christ will be a sudden unexpected event for many, those who are alert and watching will not be caught unaware.
We see two groups listed in this passage. Those who are of the light and day, and those who are of darkness and the night. From this we can see that the unsaved world will be taken by surprise when Jesus appears in judgement. They will not be ready, all of the signs of His soon appearance will go largely unoticed. Just like the people in the days of Noah were oblivious to what was about to occur, so too, those who are living in darkness will be caught by surprise.
Those who are of the light, the faithful, will be alert and ready. They will see the signs, and know that Christ is about to come. They will be ready to meet Him.
So remember what you have received and heard; and keep it and repent. Therefore if you do not wake up, I will come like a thief, and you will not know at what hour I will come to you. But you have a few people in Sardis who have not soiled their garments; and they will walk with Me in white, for they are worthy.
Revelation 3:3-4 NASB
Revelation records for us many events and signs that will occur prior to the thief-like appearance of Jesus Christ. Their are seven seals, seven trumpets and seven bowls of judgement that all culminate together at the final moment when the sky splits and Christ returns in power and glory. The last warning we read in relation to His sudden appearance is found in the context of the gathering of the armies for the battle of Armageddon.
The sixth angel poured out his bowl on the great river, the Euphrates; and it dried up, so that the way would be prepared for the kings from the east. And I saw coming out of the mouth of the dragon and out of the mouth of the beast and out of the mouth of the false prophet, three unclean spirits like frogs; for they are spirits of demons, performing signs, which go out to the kings of the whole world, to gather them together for the war of the great day of God, the Almighty. ("Behold, I am coming like a thief. Blessed is the one who stays awake and keeps his clothes, do that he will not walk about naked and men will not see his shame.") And they gathered them together to the place which in Hebrew is called Har-Magedon
Revelation 16:12-16 NASB
Any Christian alive at this point in history has lived through the most intense three and one half years of time. They have witnessed the signs that have occured over the previous seven years and are looking up because their redemption is drawing near.
Take note of the fact that this is not an event that happens before the tribulation! Popular dispensational theology teaches that Jesus comes like a thief to gather the saints in a secret rapture, removing them from the earth before the tribulation begins. What we have just read contradicts this erroneous teaching. As the armies of the world are gathering for the final battle, the warning still stands. Jesus has not yet come like a thief, we must remain vigilant.
The rest of the world will be eating, drinking, marrying, and giving in marriage. They have taken the mark. They can buy and sell. No one is persecuting them, in fact, they worship the beast that is persecuting Christians. They will cheer as the antichrist invades Israel. Yes, as these events all unfold they will be caught by surprise when Jesus unexpectedly appears. By the time dread overtakes them it will be too late.
"But when these things begin to take place, straighten up and lift your heads, because your redemption is drawing near."
Luke 21:28 NASB
What things are Jesus referring to? The events leading up to His return. The things He has just mentioned in the previous verses (Luke 21:10-27).
"Be on guard, so that your hearts will not be weighted down with dissipation and drunkenness and the worries of life, and that day will not come on you suddenly like a trap; for it will come upon all those who dwell on the face of all the earth. But keep on the alert at all times, praying that you may have the strength to escape all these things that are about to take place, and to stand before the Son of Man."
Luke 21:34-36 NASB
We must be prayerfully alert. Our strength comes from God. Many do not expect to see these days. They believe that they will be long gone, taken up when Jesus comes like a thief to rapture them. But here we see that we must have the strength to endure, to hold fast without giving in, as the events of the last days unfold around us. Our focus must be on Christ, we must look up expectantly, waiting for His sudden appearance. How tragic for one to be this close, only to give up under pressure.