THE SIXTH TRUMPET BRINGS THE SECOND TERROR
This will be the most destructive trumpet. There had been 1/4th the population had already been slain, Rev_6:7-8, Now another 1/3 was about to die. Half of the worlds people will have perished by the time this trumpet has blown. Now the demons are about to be let loose.
Rev 9:13 Then the sixth angel blew his trumpet, and I heard a voice speaking from the four horns of the gold altar that stands in the presence of God. Rev 9:14 And the voice said to the sixth angel who held the trumpet, "Release the four angels who are bound at the great Euphrates River." Rev 9:15 Then the four angels who had been prepared for this hour and day and month and year were turned loose to kill one-third of all the people on earth.
The four horns were mentioned in Exo_27:2. The four angels were not heavenly angels theses were fallen angels that had been held back by God until the 6th trumpet would sound.
From Learn The Bible by David Reagan; This passage deals with the sixth trumpet and what is called the second woe. The three woes refer to Revelation 8:13And I beheld, and heard an angel flying through the midst of heaven, saying with a loud voice, Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the trumpet of the three angels, which are yet to sound! where an angel cries, "Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the trumpet of the three angels, which are yet to sound!" The last three trumpets bring special woes to the inhabitants of the earth. The second of these woes deals with the loosing of four very special angels
Also from Learn The Bible by David Reagan as to why the Euphrates river; "Why they are bound in the Euphrates is a bit of a mystery. A couple of details about the Euphrates are significant. First, the Euphrates was the farthest eastern boundary of the land promised to Israel Genesis 15:18, Deuteronomy 1:7;Those crossing the Euphrates going east were definitely leaving the promised land. Second, the Euphrates River is especially connected to Babylon 2Kings 24:7, Jeremiah 46:2 and Babylon is prominent in the book of Revelation (Revelation 14:8;16:9, 17:5, 18:2, 10, 21). Beyond this, much is speculation. Are these fallen angels connected to Mystery Babylon? Did they commit earlier sins for which they were bound? I cannot tell. We are told what part God wants us to know at this time. The rest will be revealed when God sees fit."
Rev 9:16 I heard the size of their army, which was 200 million mounted troops. Rev 9:17 And in my vision, I saw the horses and the riders sitting on them. The riders wore armor that was fiery red and dark blue and yellow. The horses had heads like lions, and fire and smoke and burning sulfur billowed from their mouths.
As mentioned above half of the population of the earth is killed.
Rev 9:18 One-third of all the people on earth were killed by these three plagues—by the fire and smoke and burning sulfur that came from the mouths of the horses. Rev 9:19 Their power was in their mouths and in their tails. For their tails had heads like snakes, with the power to injure people.
Sulfur Gen_19:24 Was used on Sodom and Gomorrah. Sulfur and Snakes represent the wrath of God. Rev_14:10; Isa_30:33; Isa_34:9 Does anything smell worse that tar and sulfur etc. Somehow I do believe that those smells will not be present when we are with the Lord.
Rev 9:20 But the people who did not die in these plagues still refused to repent of their evil deeds and turn to God. They continued to worship demons and idols made of gold, silver, bronze, stone, and wood—idols that can neither see nor hear nor walk! Rev 9:21 And they did not repent of their murders or their witchcraft or their sexual immorality or their thefts.
At this point there appears to be few that will repent. We have a lot of chapters to go so we will see. But if it were me I would have removed all of them. We do have a merciful God praise the Lord.