Rev 6:12-17

THE GREAT DAY OF THEIR WRATH
This is “the Great Day” referred to in Joel 2, Matt 24, Acts 2, and also by Jude. It is the Great battle of Armageddon that ends man’s existence.  The sixth seal, sixth trumpet, and sixth bowl of wrath all refer to this Great Day of God’s wrath.
12 I saw when he opened the sixth seal, and there was a great earthquake. The sun became black as sackcloth made of hair, and the whole moon became as blood. 13 The stars of the sky fell to the earth, as a fig tree drops its unripe figs when it is shaken by a great wind. 
Rev 6:12
a great earthquake – the expression “earthquake” is used in Rev 11:13, and Rev 16:18: an earthquake represents war in the Book of Revelation. The “earth” means the people, and a “quake” is their shaking in war. The Reformation religious wars, that are called “an earthquake” in Rev 11:13, lasted from 1524 to 1628, and killed “a tenth of the City.” The earthquake described here in Chapter 6, is the Battle of Armageddon, and is described in Rev 16:18 (the sixth bowl of wrath), as “an earthquake such as there had not been since man came to be upon the earth.” This war will kill 1/3 of mankind as mentioned in Rev 9:15 (the sixth trumpet).

the sun became black, and the whole moon became like blood – Joel said: “the sun will be turned into darkness and the moon into blood, before the great and awesome Day of the Lord” (Joel 2:31).

Rev 6:13
and the stars of the sky fell to the earth – as in Matt 24:29, “the sun will be darkened, and the moon will not give its light, and the stars will fall from the sky.” The meaning of this is detailed in the seventh seal, which describes the seven trumpets, the darkening of the kingdom of heaven, and the falling of angels. This must happen before the battle of Armageddon which is about to be described. The sixth seal describes “the Day of the Lord.”
14 The sky was removed as a scroll when it is rolled up. Every mountain and island were moved out of their places. 
Rev 6:14
the sky split apart like a scroll – this is also Isaiah’s vision, in Isa 34:4. If ever there was a glimpse into the effect of an atomic bomb, this would be it. God takes the side of the “king of the South,” (Dan 11:40), to destroy “Gog” (the king of the North) in this great battle, that is best described in Ezek 38. Zech 14:12 says: “their flesh will rot while they stand on their feet, and their eyes will dissolve in their sockets.”


(US Government photo: “Ivy King” blast, 16 Nov 1952)
15 The kings of the earth, the princes, the commanding officers, the rich, the strong, and every slave and freeman, hid themselves in the caves and in the rocks of the mountains. 16 They told the mountains and the rocks, “Fall on us, and hide us from the face of him who sits on the throne, and from the wrath of the Lamb, 17 for the great day of their wrath has come; and who is able to stand?”
Rev 6:17
the great Day of their wrath – this is the wrath of both Christ and God, as we read in 2 Thess 1:7; Christ will come with His Angels, in flaming fire dealing out retribution. We can also see the Spirit of Christ as the warrior, the Angel of God, whose feet stand on the Mount of Olives in Zech 14:4.