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.
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).