Note 18 at 1 Th. 5:2: The terminology "the day of the Lord" is very important. "The day of the LORD" was used 19 times in the Old Testament (Isa. 2:12; 13:6, 9; Ezek. 13:5; 30:3; Joel 1:15; 2:1, 11, 31; 3:14; Amos 5:18 [twice], 20; Obed. 1:15; Zeph. 1:7, 14 [twice]; Zech. 14:1; Mal. 4:5). "The day of the LORD'S anger" was used three times (Lam. 2:22; Zeph. 2:2-3). "The day of the LORD'S vengeance" was used once (Isa. 34:8) as was "the day of the LORD'S wrath" (Zeph. 1:18). "The day of the Lord GOD of Hosts" was used once in Jeremiah 46:10. Each one of these passages is speaking of the outpouring of the Lord's wrath on the ungodly.

In the New Testament, there are five times when "the day of the Lord" is used (Acts 2:20; 1 Cor. 5:5; 2 Cor. 1:14; 1 Th. 5:2; 2 Pet. 3:10). Each one of these references is also clearly speaking of God's wrath on the ungodly.

No doubt "the day of the LORD" could also be linked with other scriptures such as Revelation 16:14 which speak of "?the battle of that great day of God Almighty" (2 Pet. 3:12; 1 Jn. 4:17; Rev. 6:17).

Therefore, this terminology is very clearly referring to a time when God brings judgment on the ungodly. The Word of God has many examples of God's judgment on the ungodly, but it also clearly depicts a future time referred to as "the day of the LORD" when world-wide judgment will be executed as never before.

Today we see men blaspheme God and live in ways that will not be tolerated in "the day of the Lord." That's because we are living in the Church age which is a day of grace. That's not to say there has never been grace until the establishment of the Church. No, the Word of God is full of God's grace in the Old Testament. But during the present time of the Church, we see God's grace manifested towards mankind in a way that it never was before.

Likewise, there has been judgment from God on the ungodly throughout history. But there is coming "the day of the Lord" that will make the flood and the destruction of Sodom and Gomorrah seem mild in comparison.

Isaiah prophesied about "the day of the Lord" this way: "Howl ye; for the day of the LORD is at hand; it shall come as a destruction from the Almighty. Therefore shall all hands be faint, and every man's heart shall melt: And they shall be afraid: pangs and sorrows shall take hold of them; they shall be in pain as a woman that travaileth: they shall be amazed one at another; their faces shall be as flames. Behold, the day of the LORD cometh, cruel both with wrath and fierce anger, to lay the land desolate: and he shall destroy the sinners thereof out of it.

For the stars of heaven and the constellations thereof shall not give their light: the sun shall be darkened in his going forth, and the moon shall not cause her light to shine. And I will punish the world for their evil, and the wicked for their iniquity; and I will cause the arrogancy of the proud to cease, and will lay low the haughtiness of the terrible. I will make a man more precious than fine gold; even a man than the golden wedge of Ophir. Therefore I will shake the heavens, and the earth shall remove out of her place, in the wrath of the LORD of hosts, and in the day of his fierce anger" (Isa. 13:6-13).

Notice that in Isaiah's prophecy, he speaks of the darkening of the sun, moon, and stars just as Joel did in Joel 2:31. Jesus also referred to this same thing in Mark 13:24-26 and related it to His second coming. Paul uses the same analogy in 1 Thessalonians 5:3 that Isaiah used in verse 8. This "day of the Lord" is no doubt the second return of the Lord when He executes judgment on the ungodly.

Note 19 at 1 Th. 5:2: The illustration that Paul is drawing on is the suddenness and surprise of a thief. The second coming of the Lord will come upon the world unawares so that they will not have time to do anything about it. Jesus used this same illustration (Mt. 24:43; Lk. 12:39).