Alcuin of York — on Rev 6:12 (COMMENTARY ON REVELATION)

“And I saw when he had opened the sixth seal: there was a great earthquake, and the sun became black as sackcloth of hair: and the moon became as blood. By the earthquake we should understand the last persecution under the Antichrist. It is called great because, according to the Lord's saying, there will then be a tribulation such as has never been, neither shall be. [Matt. 24:21] The sun is Christ, according to this: Unto you that fear God, the Sun of justice shall arise. [Cf. Mal. 4:2] This sun will be darkened for the last people when those who looked as though they were shining in the body of Christ fall into the darkness of overt error. The sun may also indicate the shining life of those who preach. So in the last times the sun will be as sackcloth of hair because the shining life of those who preach will appear rough and despicable in the eyes of the reprobates. Indeed cilice is fit for criminals and sinners. By the moon turned into blood we recognize the holy Church stained in the elect by the blood of suffering. It is said to be entirely stained because no one who remains in the faith of the Mediator will be immune from that last persecution; whence Joel says, The sun shall be turned into darkness, and the moon into blood: before the great and manifest day doth come. [Variant of Joel 2:31 close to the LXX version, where it is numbered 3:4]”