"1 Thes. 4:13-18 describes the Rapture. . . . In 1 Thes. 5:1, he changes topics. This is proven by his use of two little Greek words, peri de. These two words . . . could be translated, "But concerning" or "Now about." . . . . Every time Paul uses these two words, they always denote a change in subject matter. In 1 Thes. 4:13-18, the subject matter is what happens at the Rapture. But in 1 Thes. 5:1-11, he introduces a new subject, a different event, the Day of the Lord."
It should also be clear that the Day of the Lord differs from the Rapture, in that, the Rapture is a joyous event, and the Day of the Lord is "a time of destruction" (Isa. 13:6); "a day of vengeance" (Jer. 46:10); "a solemn day of terrors" (Lam. 2:22); "the time of the heathen" (Ezek. 30:3); "a destruction from the Almighty" (Joel 1:15); "darkness and not light" (Amos 5:20); a day of recompense (Obed. 1:15); "the fierce anger of the LORD" (Zeph. 2:2); a day of great loss (Zech. 14:1); and in the New Testament, "the heavens shall pass away with a great noise, and the elements shall melt with fervent heat" (2 Pet. 3:2).
The Rapture is the removal of God's true believers prior to the certain travail of the rebirth of Israel. Isaiah wrote, "Like as a woman with child, that draweth near the time of her delivery, is in pain, and crieth out in her pangs; so have we been in thy sight, O LORD. We have been with child, we have been in pain, we have as it were brought forth wind; we have not wrought any deliverance in the earth; neither have the inhabitants of the world fallen" (Isa. 26:17-18). Jesus spoke of the signs at the beginning of the Tribulation as being "the beginning of sorrows." The Greek word, ὠδίν (ōdin), means "the pain of childbirth, travail pain, birth pangs." In essence, this metaphor is describing the birth, or better perhaps, the rebirth of Israel. For following "the beginning of sorrows" comes the Abomination of Desolation, which occurs half way through the seven-year Tribulation, which is said to be appointed unto Daniel's people (Dan. 9:24-27; 12:11; Matt. 24:15; Mk. 13:14; Rev. 12 -13). Israel, seeing this event take place, have their blindness to the truth removed, and they realize that Jesus was their Messiah, and all Israel is saved! Paul wrote,
" For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: for this is My covenant unto them, when I shall take away their sins. As concerning the gospel, they are enemies for your sakes: but as touching the election, they are beloved for the fathers' sakes. For the gifts and calling of God are without repentance" (Rom. 11:25-29).
The Tribulation, for Israel, will be an eye-opening experience!