Then he goes on with the prophecy, which has in it also something terrible. "And I will show wonders in heaven above, and signs in the earth beneath." In these words he speaks both of the judgment to come, and of the taking of Jerusalem.
"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.
For Peter says, "It is the third hour of the day." And what of that? Is it not at the third hour that one becomes drunk? Certainly, that was not in accordance with their intention: for they did not truly think that of them, but said it while jeering and mocking. He made them formerly more careful; but these things happened at the third hour, not simply. For then the brilliance of the fire is shown, when men are neither at work nor at their meal, when the day is bright, when all are in the marketplace. Then he brought forward the prophecy of Joel, nowhere mentioning Christ here, and of the signs of which they were eyewitnesses, or that this had been his promise. For if he had said this, he would have overturned everything and exposed it to scorn; but he first introduces the Father who had promised these things to them through the prophet, and removes the envy; not, he says, to the apostles only, but to every flesh, clearly to those believing sincerely, and with character. For he does not mean the one who says to me, he says, "Lord, Lord," (Matt. 7:21) but the one living a life of the best sort and doing this. He does not add this, making the word of the promise more burdensome and making it light, because the request alone suffices for salvation.
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.
Blood and fire and vapor of smoke. The blood of the Lord’s side, the fire of the Holy Spirit, the vapor of compunction and weeping. For as from fire comes smoke, so from the ardor of the Holy Spirit proceeds compunction. For it remains to believe that blood flowed from a dead body in a living stream, which is against the nature of our bodies, was done as an indication of a sign. For what other purpose, unless for our salvation and life, which indeed springs from His death? The illumination of the faithful can also be understood in the fire, and the blindness of the Jews who did not believe in the vapor of smoke. Hence, the Lord, about to give the law, descended in fire and smoke, because He illuminates the humble through the brightness of His manifestation, and darkens the eyes of the proud through the obscurity of error.
Blood, and fire, and vapor of smoke. About fire and smoke it has been said in the previous book: he speaks of blood not only of the Lord’s wounds, but also of the Lord’s sweat, when, praying before the betrayal, His sweat became like drops of blood falling to the ground. This is numbered among the divinely wrought signs, because it is proved not to be found in the custom of human nature. It is therefore a sign, because it signified that the whole world would be cleansed by the blood of the Lord, so that just as the tabernacle or temple was at some point consecrated to the Lord with the blood of victims, so now through the whole world the faithful people would be dedicated to Him as a holy house by His own blood, and not only in Jerusalem would be a place for prayer, but in every place of His dominion, the elect would lift their hands through pure prayers to the Lord.
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.
[AD 407] John Chrysostom on Acts 2:19