v1-7: The first three bowls are poured out. Those who have the mark of the beast receive the first judgment. These judgments are not the actions of a capricious God, revelling in suffering, but in a righteous God, honouring His own word, and demonstrating His own character. There is judgment on those who have shed the blood of God's servants, and therefore receive their due recompense. God's course of action is not doubted, for all agree, led by the altar of God, "Yes, Lord God Almighty."
v8-11: The fourth and fifth angels pour out their bowls. Scorching heat is followed by intense darkness, but men refuse to repent and give God glory. The fact that the judgments do not actually kill them, provides men with an opportunity to repent. Here again is God's mercy, and His restraint in judgment.
We note that the first four bowls affect the land and waters, sun and seas, as in 8.7-13; all areas of creation are thus affected.
v12-14: The Euphrates is dried up, preparing the way for the great army, gathered from throughout the world to meet at Armageddon, see 19.19; here the beast, with the kings of the earth, and their armies, gather together.
The source of the beast's power is made manifest; evil spirits, demons, performing miraculous signs. There is no doubt that they are opposed to the true God.
v15: The godly respond in watchfulness and holiness; there are false prophets, counterfeit miracles, spirits of demons. Not everything that looks wonderful is good. The Lord Jesus commanded His followers to be ready, Matt 24.44.
It is said that if a priest or Levite fell asleep on night watch (see comment at Luke 12.38), the punishment was to have his clothes set on fire! But there is no historical record of this occurring.
v16: The kings of the whole world gather at Armageddon. They are inspired by the dragon, the beast, the false prophet. They unite to oppose the Lamb and His people. Armageddon (Megiddo) was the sight of previous battles; Judg 5.18; 2 Kings 23.29. For a Jew, the very name carried significance.
v17-21: The seventh angel brings a severe earthquake, affecting the "great city" and "the cities of the nations." Islands and mountains disappear, and hailstones fall; and men curse God, instead of repenting.