The Day of the Lord

The Day of the Lord is a point in time when God signals He is about to take back the earth from Satan's rule.  Christ describes this day in Matthew 24:29a, with "But immediately after the tribulation of those days..." (meaning after the Great Tribulation from v21) and proceeds to paraphrase Isaiah which states on this fearful day "the stars of heaven and their constellations will not flash forth their light; the sun will be dark when it rises, and the moon will not shed its light.  This I will punish the world for its evil..." (Isaiah 13:10, 11a).

This parallels the oft quoted Day of the Lord passage in Joel that says "The sun will be turned into darkness, and the moon into blood, before the great and awesome Day of the Lord comes" (Joel 2:31, emphasis added).  Later, Joel also describes this sign that precedes the Day of the Lord in more detail: "For the Day of the Lord is near in the valley of decision.  The sun and moon grow dark, and the stars lose their brightness" (Joel 3:14b, 15).

These passages show that the sign of the end of the age, before the Day of the Lord, will be the sign the Lord gave to Joel, Isaiah, John in Revelation at the sixth seal opening, and also the same sign Christ gave His disciples so they would know the event signalling the "the end of the age".

Scripture clear states what the sign (the celestial disturbances) will be and when it will occur--immediately after the tribulation of those days" (Matthew 24:29a) but "before the great and awesome Day of the Lord" (Joel 2:31).

Christ links the sign signalling the end of the age being "immediately after the tribulation" (Matthew 24:29a) with the sign prophesied in the Old Testament announcing the Day of the Lord, which will only occur when the Great Tribulation by the Antichrist is "cut short" by Christ's return.  Here's the full passage from Matthew 24:29-31:

Matthew 24:29-31
“But immediately after the tribulation of those days THE SUN WILL BE DARKENED, AND THE MOON WILL NOT GIVE ITS LIGHT, AND THE STARS WILL FALL from the sky, and the powers of the heavens will be shaken. 30“And then the sign of the Son of Man will appear in the sky, and then all the tribes of the earth will mourn, and they will see the SON OF MAN COMING ON THE CLOUDS OF THE SKY with power and great glory. 31“And He will send forth His angels with A GREAT TRUMPET and THEY WILL GATHER TOGETHER His elect from the four winds, from one end of the sky to the other.

Granted some believe there have been instances in history where God has exercised judgment on the earth and has declared that judgment as being a Day of the Lord.  Regardless of that perspective, I believe that someday there will be a final Day of the Lord that will affect the whole earth.