Revelation 16:1–7 reports the beginning of the bowl judgments which were predicted in Revelation 15:5–8. The first and second judgments resemble the plague of boils and the plague of blood that God brought upon the Egyptians when Pharaoh refused to let the Hebrews leave Egypt (Exodus 7:19–21; 9:8–12). The third judgment turns the water sources into blood. The second and third judgments resemble the third trumpet judgment (Revelation 8:8), but their intensity is greater. A break occurs in 16:5–7 as an angel reflects on the first three bowl judgment and affirms that God is just to judge the wicked.
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Revelation 16:7 BibleRef.com
7 I heard the altar saying, “Yes, Lord God, the Almighty, true and righteous are your judgments.”