In Chapter 8, John describes the breaking of the seventh seal, which ushers in the Day of the Lord. When the seventh and final seal is broken, the seven-sealed scroll, or Large Scroll, described in Revelation 5, will unroll. The Large Scroll contains the seven trumpet and seven bowl judgments.
The Trumpet judgments are Phase 1, or the beginning of God’s wrath. Many of God’s elect will still be on the earth during the trumpet judgments but will remain untouched by God’s wrath, even as the Israelites were untouched by the plagues which went around them in Egypt. The trumpet judgments may be centered in the Middle East in order to directly influence Israel. Only one-third of the earth is affected by the seven trumpets. This would explain why the 144,000 servants from Israel are sealed just before the start of the trumpet judgments so as to pass through them unharmed.
The Day of the Lord will be a time of unprecedented spiritual warfare. Jesus Christ and Antichrist, both on Earth, will be battling for the souls of the undecided, those who have not yet chosen either Jesus or Satan, embodied in Antichrist. During this time, three forces will be preaching the Word of the Lord: (1) the Two Witnesses (See Rev 11:3-6); (2) the 144,000 Jews, who will witnesses of God’s faithfulness to the nation Israel (See Rev 14:1-5); and (3) an angel sent by God to preach the gospel to every living creature on earth (See Rev 14:6-10).
As the seven trumpets are blown, God’s judgment begins to fall upon the earth. Each trumpet judgment contains an element of the supernatural, unlike anything accompanying the breaking of the seals. These supernatural occurrences include abnormal occurrences of fire, waters turning to blood, burning asteroids colliding with the earth, the striking of the sun, moon, and stars, locusts released from the bottomless pit, and angels sent to kill a third of mankind.
Note that the seven trumpets are a call to salvation; during the Day of the Lord another period of evangelism will occur for those who have not taken the mark of the beast.Like the 144,000, those saved during the Day of the Lord will have rejected Antichrist but not accepted Jesus at the time of the Rapture.Indeed, in many cases the Rapture itself (the Second Coming of Christ) will convince non-believers that Jesus Christ is Lord. As such, the Day of the Lord will be the time of final harvest of believers.