After the time of war, the man of sin declares himself to be God. Those who don’t worship him as such are to be killed. The mark and the image will force people to make that choice quickly. After enough time has passed, and everyone has made their decision as to who they worship, the sixth seal is opened. The sixth seal is when God intervenes in the war against the saints. The persecution becomes less intense because those who chose to worship the man of sin start to come under judgment.
The opening of the sixth seal announces the coming of the time of God’s wrath. This will be accomplished through a series of seven plagues which are revealed when the seventh seal is opened. The seven plagues are carried out by seven angels according to Revelation 15. Each plague begins with the sounding of a trumpet and is brought to its fullness when a bowl is poured out. They will only affect those who utilize the mark of the beast and worship the image.
When the Lamb broke the seventh seal, there was silence in heaven for about half an hour. And I saw the seven angels who stand before God, and seven trumpets were given to them. And the seven angels who had the seven trumpets prepared themselves to sound them. Revelation 8:1-2,6
The first four plagues begin as a fraction of what they will become. They affect the natural world directly and their purpose is to convince those who worship the man of sin that they are making a mistake. They are a direct challenge to his claim of being God so that those who were deceived by him might know the truth and repent.
The last three plagues are called “woes” and affect people directly. The first two woes are the final call to repentance before Jesus returns at the third woe to destroy the unrepentant. This is what happens when the seventh plague, the final woe, begins:
And they will see the Son of Man coming on the clouds of the sky with power and great glory. And He will send forth His angels with a great trumpet and they will gather together His elect from the four winds, from one end of the sky to the other. 24:30b-31 NASB
The reason that the first six plagues are not mentioned in Matthew 24 is because Jesus is describing for His disciples the signs that they are to look for to know that His return is near. The plagues will only affect those who utilize the mark of the beast and worship the image. They are not signs for believers to look for since believers will reject the mark and the image at any cost.