Revelation 16:15? What is meant by this?
The return of Jesus the Christ is likened to the coming of a thief in the night. Two passages use the wording “a thief in the night”: “But know this, that if the goodman of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up.” Matthew 24:43
and “For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.” 1 Thessalonians 5:2
In Matthew 24, Jesus speaks of His second coming at the end of the tribulation. Paul calls it “the day of the Lord” in 1 Thessalonians 5. This is a day of divine retribution featuring astronomical upheaval and the visible “sign of the Son of Man” in the heavens (Matthew 24:29–30). Jesus says it will happen “after the tribulation of those days” (verse 29), a description that distinguishes this event from the rapture, which happens before the tribulation.
How is the second coming going to be like a thief in the night? The key element of Jesus’ comparison is that no one will know when He will return. Just as a thief catches a household by surprise, Jesus will catch the unbelieving world by surprise when He returns in judgment. People will be “eating and drinking, marrying and giving in marriage” (Matthew 24:38), just as if they have all the time in the world. But then, before they know it, Judgment Day will be upon them (verses 40–41). Paul puts it this way:
“For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.” 1 Thessalonians 5:3
The believer does not fear this swift and sudden judgment; the “thief in the night” will not catch Christians by surprise. Christians are in a separate category:
“But ye, brethren, are not in darkness, that that day should overtake you as a thief.” 1 Thessalonians 5:4