Revelation 16:3-7

The second angel poured out his vial, &c.— This vial is poured out upon the sea, and the sea becomes as the blood of a dead man, or as congealed blood; and, in like manner, under the second trumpet, ch. Revelation 8:8 the burning mountain was cast into the sea, &c. The third vial (Revelation 16:4.) is poured upon the rivers, &c. and in like manner under the third trumpet, ch. Revelation 8:10 the burning star fell upon the rivers, &c. There is a close connection between the two vials; and the effects are similar to the first plague of Egypt, Exodus 7:17. Seas and rivers of blood manifestly denote slaughter and devastation; and hereupon, Revelation 16:5 the angel of the waters celebrates the righteous judgments of God in adapting and proportioning the punishment of the followers of the beast to their crime; for no law is more just and equitable, than that they who have been guilty of shedding the blood of saints and prophets, should be punished in the effusion of their own blood. Another angel out of the altar declares his assent in the most solemn manner, Revelation 16:7.