"At the sight of them, nations are in anguish; every face turns pale. They charge like warriors; they scale walls like soldiers. They all march in line, not swerving from their course. They do not jostle each other; each marches straight ahead. They plunge through defenses without breaking ranks. They rush upon the city; they run along the wall. They climb into the houses; like thieves they enter through the windows." NIV translation
This passage describes an unstoppable wall of locusts that ravaged the land in the prophet's day but is even more terrible in the days that are to come. Like an army of robots, they are not distracted from their mission and they go everywhere to torture the people. They are not stopped by walls or anything else and they do not distinguish between the rich and the poor as all homes are entered.
"Before them the earth shakes, the sky trembles, the sun and moon are darkened, and the stars no longer shine." NIV translation
These same events are described in Revelation 8 as they are unleashed when the fourth trumpet is blown.
"The Lord thunders at the head of his army; his forces are beyond number, and mighty are those who obey his command. The day of the Lord is great; it is dreadful. Who can endure it?" NIV translation
This verse describes the same events that John described in Revelation 19. The nations of the earth have gathered for battle in hopes of overtaking the city of Jerusalem but they are opposed by the army of God led by Jesus Christ.
"'Even now,' declares the Lord, 'return to me with all your heart, with fasting and weeping and mourning.'" NIV translation
What is the purpose of this judgment and the great tribulation that is to come? We see, here, that the purpose is for Israel to repent and return to the Lord.