Acts 2:20

For at that time the trumpet shall sound, and awake those that sleep from the lowest parts of the earth, righteous and sinners alike. And every kindred, and tongue, and nation, and tribe shall be raised in the twinkling of an eye; and they shall stand upon the face of the earth, waiting for the coming of the righteous and terrible Judge, in fear and trembling unutterable. For the river of fire shall come forth in fury like an angry sea, and shall burn up mountains and hills, and shall make the sea vanish, and shall dissolve the atmosphere with its heat like wax. The stars of heaven shall fall, the sun shall be turned into darkness, and the moon into blood. The heaven shall be rolled together like a scroll: the whole earth shall be burnt up by reason of the deeds done in it, which men did corruptly, in fornications, in adulteries, and in lies and uncleanness, and in idolatries, and in murders, and in battles. For there shall be the new heaven and the new earth.

these are the signs of the end of the world.

"Before that great and notable day of the Lord come." For be not confident, he means to say, because at present you sin with impunity. For these things are the prelude of a certain great and dreadful day. Do you see how he made their souls to quake and melt within them, and turned their laughter into pleading for acquittal? For if these things are the prelude of that day, it follows that the extreme of danger is impending.

"Blood and fire, and vapor of smoke." Observe how he describes the capture. "The sun shall be turned into darkness, and the moon into blood." This results from the internal affection of the sufferers. It is said, indeed, that many such phenomena actually did occur in the sky, as Josephus attests. At the same time the Apostle strikes fear into them, by reminding them of the darkness which had lately occurred, and leading them to expect things to come.

The worst to come first; namely, the inhabitants to be taken, and then the city to be razed and burnt. Then he dwelt upon the metaphor, bringing before the eyes of the hearers the overthrow and the taking. "The sun shall be turned into darkness, and the moon into blood." What means, the moon turned into blood? It denotes the excess of the slaughter. The language is fraught with helpless dismay.

the Church, shall be darkened, because in those tremendous temptations and tribulations which shall be in the end of the world, many who had seemed as bright and as firm as the sun and the stars shall fall from the faith.

Now, "The sun shall be turned into darkness," and the preceding, "blood and fire and vapor of smoke," these refer to the coming judgment. More appropriately and specifically they speak of Jerusalem and its then captivity, as is shown by the nature of those suffering. Likewise, according to Josephus, many such things foreshadowed the destruction of Jerusalem. That the moon is said to be turned into blood signifies the excess of slaughter, being nearer to the earth and able to suffer this from the exhalation of blood. As for, "before the great and notable day of the Lord shall come," is terrifying and alarming because of the expected dangers. For he says, do not be confident in the fact that you now sin with liberty; but know that these are preludes to that great and dangerous retribution of deeds which will follow, adding, "And everyone who shall call upon the name of the Lord shall be saved." (Rom. 10:13) For Paul the apostle says this was said concerning Christ: but now, since there is no opportunity for that here, in a certain exemption of speech he postponed this.

The sun shall be turned into darkness, and the moon into blood. This is believed to have been partly fulfilled during the Lord's Passion, and partly to occur before the great day, that is, the Day of Judgment. For at that time the sun was darkened, but the moon, turned into blood, could not plainly appear to men, since it was (as it happens during Passover) the fifteenth day, and during the day it was hidden from mortal sight by the obstruction of the earth.

The sun will be turned into darkness. The name of darkness in Greek is read in the singular number, that is, σκότος, which the Latin translator necessarily rendered in the plural as tenebras because he could not express it in the singular. I thought it necessary to mention this so that anyone who reads this among the people of the Angles might know that it is not necessary, because of the authority of the Latin language, to render "darkness" in their own speech in the plural; rather, it should be in the singular, as this can just as easily be done owing to the authority of the Greek, from which it was translated into Latin scripture.

With these words the prophet clearly foretells in advance both the future judgment, and the destruction of Jerusalem, and the captivity of the Jews, and the events that were to take place at the cross of Christ, and finally, what happened to the Jews as a result of the Roman war, when much blood was shed by the Romans in Judea, when smoke billowed from the burning of cities and villages. Through this the Jews bore punishment for their audacity against Christ, an audacity which even the sun itself could not endure and closed its eye, its luminous power, and the moon changed its silver-like appearance into a red light. They say, however, that many similar phenomena occurred in the sky also during the destruction of Jerusalem; so testifies Josephus Flavius. Moreover, with the words "the moon" shall be turned "into blood," the prophet also points to the excessive cruelty of the slaughter (that is, the crucifixion of the Lord). But why does this happen at the third hour? To show the miraculous nature of this phenomenon: the brilliance of fire is seen in the middle of a bright day, when everyone is in the public square! However, the composer of liturgical hymns understands what was said by the prophet thus: blood signifies the incarnation, fire signifies the Divinity, the vapor of smoke signifies the Holy Spirit, who overshadowed the Virgin with His descent and filled the world with fragrance, and by the day of the Lord he means the day of the resurrection.