Verses 3-6: The second bowl was poured directly into the sea and the third bowl was poured directly into the rivers and springs which are the earths natural sources of drinking water. In each case the water was turned to blood probably meaning it turned red in color until it resembled blood in appearance. We can only speculate on what will cause this phenomenon. It might be the growth of red algae or some other organism due to extreme climate change. We will shortly discover as the fourth bowl is poured out (vs 8, 9) that the sun is scorching the earth during this time. Such heat will certainly cause water temperatures to rise and this may help explain the statement in verse three that every living thing in the sea died. But regardless of what causes the red color the prophetic symbolism is unmistakable. Verse six states it outright, ...they poured out the blood of saints and prophets, and you have given them blood to drink. They deserve it. Just as Abels blood cried out from the ground following his murder by Cain (Ge 4:10), the waters of the earth will cry out on behalf of all the innocent believers murdered by the antichrist. Its as if the earth itself hemorrhages as a witness to their deaths.
Verses 3-6 (continued): In verse five the angel who poured wrath on the fresh waters affirms the justice behind Gods actions. He speaks of God being righteous, eternally existent and holy, and says these judgments prove His righteousness. To be righteous means He gives justice without prejudice or partiality (W.E. Vine, righteous). He does what is right. Because God is righteous His laws and decrees are also righteous. Though the earth at this time is experiencing devastating calamities it isnt because God has been unfair or become unduly angry. It is because He is completely fair.
Verse 7: Since altars dont talk, the voice coming from the altar of incense (6:9; 8:3, 5; 14:18) must be the voice of the souls underneath the altar (6:9, 10) who had earlier called upon God to give them justice for their martyrdom. They had asked, How long, O Lord, holy and true, will You refrain from judging and avenging our blood on those who dwell on the earth? (6:10). And now as the waters turn to blood the martyrs declare Gods judgments to be true, meaning He has faithfully kept His promise to give them justice, and righteous, meaning He is justly giving the earth what it deserves.
Revelation 16:8, 9
Verses 8, 9: The fourth angel poured his bowl on the sun causing it to burn humans with great heat. Again were not told what natural forces, if any, caused this solar disaster, but it results in the earths atmosphere warming to the point that people are miserable and angrily blaspheme God. No one repents even though they recognize God is the source of their crisis. By this state in the final seven years unbelievers have become completely seared in their conscience (1Ti 4:2). This dramatic increase in solar radiation may also help explain an interesting statement John made in Revelation 7:14-17 about the believers who came out of the great tribulation. In that vision he saw God comforting them in heaven and in his description he specifically noted they will not thirst anymore (because the waters have turned to blood?), nor will the sun beat down on them, nor any heat (because the sun is scorching men with fire?).
Verse 10: The fifth bowl is poured directly onto the antichrists kingdom leaving it darkened and with people in such pain they gnaw their tongues in agony. The natural cause of this darkness is not explained, but it may be the result of the same sorts of pollution we saw produced by the first four trumpet judgments (Rev 8:7-13). Jesus said that after the tribulation of those days the sun will be darkened and the moon will not give its light and the stars will fall from the sky (Mt 24:29; Mk 13:24, 25). His words may well describe an earth in which the atmosphere is filled with smoke, dust, volcanic ash, water vapor, etc. Or God may impose a supernatural darkness similar to that which He brought upon Egypt for three days prior to the Exodus (Ex 10:21-23).
Verse 10 (continued): In the midst of this darkness people will be in great physical pain. Since darkness itself doesnt normally cause physical pain, their suffering likely results from the effects of the four previous bowls (skin sores, thirst, sunburn, heat stroke...). But regardless of its cause, suffering in the dark would make everything else far more difficult to bear. In fact, it would create a hell-like situation (Mt 8:12; 22:13; 25:30) which may well be exactly what God intends in order to give the earth a foretaste of what lies ahead for those who refuse to repent. If so, these miseries perform a dual purpose: They begin the just punishment due those who have rebelled against God, but at the same time they mercifully let these rebels experience some of the eternal conditions theyll soon face unless they repent. Even though their hearts have grown very hard it is still possible for them to repent and escape their approaching doom. Gods heart to save even one more can be seen behind all of this catastrophe.
Revelation 16:11, 12
Verse 11: In spite of unmistakable evidence that this era of earths history is coming to an end, no one repents. Their misery only increases their blasphemy toward God. Clearly, by now all who are willing to repent have done so. These final judgments and warnings have only increased their hatred toward God. Verse 12: The sixth bowl is now poured into the Euphrates River causing its waters to dry up until it no longer forms a barrier to armies moving toward Israel from the east. At the antichrists command a multinational force will assemble to attack Jerusalem (Zec 12:2, 3; 14:2). As weve already seen the sun will scorch the planet during this time and such heat might well produce a drought so severe that even this major river would dry up or be reduced in flow until military vehicles could pass over unobstructed. The Euphrates was designated by God as the northern border of the land He promised to Abraham (Ge 15:18). By drying up this river He opened a door for the enemies of Israel to attack, just as drying up the Jordan allowed Israel to begin their conquest of Canaan (Jos 3:14-17). Only in this case, His plan is not to forsake Israel, but instead to draw the antichrists army into His winepress (Rev 14:20) in order to destroy them.