The seven angels/messengers are sent to pour out the seven vials containing the wrath of God upon the earth which is where those who persecuted and killed God's people were located. The first vial was poured out upon those who had the mark of the beast and worshipped his image. The mark of the beast indicates those who supported Roman authorities and worshipped the image of Caesar. This would specifically be Jews who had said, "We have no king but Caesar", denying Jesus as they said, "crucify Him". The second angel/messenger poured his vial upon the sea and it became as blood. In Revelation, the sea represented people and this indicates the coming bloodshed that would accompany Jerusalem's destruction. The third angel/messenger poured out his vial upon the rivers and fountains of waters indicating further bloodshed. A declaration of the righteousness of the Lord for His judgment is made. The reason for His judgment is given. It is because these people shed the blood of saints and prophets. We should remember what Jesus said in Matthew 23 when He made that generation of Jews responsible for all the righteous blood shed from Abel to Zacharias. Another from the altar declares the judgments of the Lord to be true and righteous. The effect of the fourth, fifth and sixth vials being poured out are recorded by John. Go to the study to see the specifics on these actions. When the seventh vial is poured out, there is a great voice heard out of the temple of heaven from the throne and it says, "It is done." Again, go to the study and see the discussion on what this is referring to.