8 The second angel sounded, and something like a great mountain burning with fire was thrown into the sea. One third of the sea became blood,
the second trumpet, a great mountain – the great mountain in the last days is the mountain of the Lord, from Isa 2:2, and Mic 4:1. This is the true Church, the New Jerusalem; the Great Mountain we see in Rev 21:10. This is the true body of Christ, “the stone that struck the statue became a a great mountain and filled the whole earth” (Dan 2:35).
burning with fire – fire represents the holy spirit as in Rev 15:2. The spirit of God comes against the work of the beast as “a river of fire” in Dan 7:10.
thrown into the sea – the success of the true Church is described as the spirit of God entering the sea in Ezek 47:8. The outpouring of the spirit of truth brings life to some, but judgment to those who preach another gospel, as we read in Gal 1:8-9. The spirit of truth brings the hour of judgment to false teachers: “now the hour of His judgment has come” (Rev 14:6-7).
the sea became blood – this is the first plague on Egypt. Moses turned the Nile into blood (Exod 7:14-25) and all the fish died. In Rev 16:4, the second bowl of wrath, from the second Angel, is also blood on the sea. This is the same account. The meaning of the sea in the Book of Revelation is salvation/baptism, crossing the Red Sea (1 Cor 10:1-2). We can see this in Rev 15:2, “standing on a sea of glass and fire” – the elect cross the symbolic Red Sea, which is the baptism of water and Spirit.
The spiritual death of baptism/salvation here, is related to the spiritual death of communion in Rev 14:10. Those who worshiped the image of the beast and received his mark, drank “the wine of the wrath of God.” In other words, they took of the Lord’s body in “an unworthy manner” (1 Cor 11:29). The baptisms/salvation of those who worship the image of the beast and receive his mark, also result in spiritual death.