Charles Spurgeon Commentary Acts 2:14-20

"But Peter, standing up with the eleven, lifted up his voice, and spake forth unto them, [saying], Ye men of Judaea, and all ye that dwell at Jerusalem, be this known unto you, and give ear unto my words. For these are not drunken, as ye suppose; seeing it is [but] the third hour of the day. but this is that which hath been spoken through the prophet Joel: And it shall be in the last days, saith God, I will pour forth of my Spirit upon all flesh: And your sons and your daughters shall prophesy, And your young men shall see visions, And your old men shall dream dreams: Yea and on my servants and on my handmaidens in those days Will I pour forth of my Spirit; and they shall prophesy. And I will show wonders in the heaven above, And signs on the earth beneath; Blood, and fire, and vapor of smoke: The sun shall be turned into darkness, And the moon into blood, Before the day of the Lord come, That great and notable [day]." — Acts 2:14-20 (ASV)

But Peter, standing up with the eleven, lifted up his voice and said to them, You men of Judea, and all you that dwell at Jerusalem, be this known to you, and listen to my words: for these are not drunk, as you suppose, since it is but the third hour of the day. But this is that which was spoken by the prophet Joel; And it will come to pass in the last days, says God, I will pour out of my Spirit upon all flesh: and your sons and your daughters will prophesy, and your young men will see visions, and your old men will dream dreams: And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they will prophesy: And I will show wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapor of smoke: The sun will be turned into darkness, and the moon into blood, before that great and notable day of the Lord comes:

Doubtless this refers first to the siege of Jerusalem, when those strange portents were seen in the heavens, and afterwards to that far greater and more notable day of the Lord, the day of judgment, when the moon will become as blood, and the sun will become black as sackcloth of hair.