"And I heard a great voice out of the temple saying to the seven angels, Go your ways, and pour out the vials of the wrath of God upon the earth. And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image." (Revelation 16:1-2)
In the previous chapter, the preparation of the vials or bowls was completed; and now, the execution of the judgments takes place. To the seven angels, a general command is given which is immediately followed by a specific description of each plague. This divine wrath is aimed at the earth's unregenerate who have brought irrevocable damage upon themselves through the reception of the antichrist's mark. These judgments are not directed toward the tribulation saints who have found refuge in God's grace (Revelation 9:4).
The word behind noisome means bad or harmful (Greek kakoj). Extremely painful sores, abscesses or ulcers break out upon the flesh of those who have been deceived. These sores are probably open and cankerous. This physical pain is merely a foretaste of the eternal torment which awaits. In the middle of such pain and chaos, the redeemed will find great comfort in the fact that they have been preserved from wrath through belief in the precious blood of Christ. The persecutions and terrors effected by the antichrist against Christ's followers will not compare to the horrors inflicted upon the ungodly at the day of judgment.
"And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea." (Revelation 16:3)
The magnitude of this second plague boggles the mind. The water of the world's seas and oceans will be turned into blood. Some commentators consider this to be a red tide of astronomical proportions; however, in all probability, the text is speaking of literal blood (8:8, 16:4). The sight will be incredibly fearful; the stench will be unbearable; and the effect will be disastrous as every living thing in the sea dies.