When Jesus described the Great Tribulation, notice that He said, "If the Lord had not cut short those days, no one would survive":
"When you see 'the abomination that causes desolation' standing where it does not belong--let the reader understand--then let those who are in Judea flee to the mountains. Let no one on the roof of his house go down or enter the house to take anything out. Let no one in the field go back to get his cloak. How dreadful it will be in those days for pregnant women and nursing mothers! Pray that this will not take place in winter, because those will be days of distress unequaled from the beginning, when God created the world, until now--and never to be equaled again. If the Lord had not cut short those days, no one would survive. But for the sake of the elect, whom he has chosen, he has shortened them." (Mark 13:14-20)
According to this passage, the Great Tribulation (the final three and a half years of the Tribulation) will be so terrible that no-one would survive it, and therefore God has "cut short" the days of the Great Tribulation. Some people believe that God will shorten the Great Tribulation so that it will actually be less than three and a half years, but there are several problems with that view. For one thing, the Great Tribulation will last for 1,260 days, which is a very exact timeframe. Notice that if God shortens that timeframe then the Great Tribulation will not last for 1,260 days, which would contradict Revelation 12:5-6. This makes it unlikely that God will shorten the length of the Great Tribulation. For further evidence, notice what an angel did when the prophet Daniel was given some end-times prophecies:
""At that time Michael, the great prince who protects your people, will arise. There will be a time of distress such as has not happened from the beginning of nations until then. But at that time your people--everyone whose name is found written in the book--will be delivered." ... Then I, Daniel, looked, and there before me stood two others, one on this bank of the river and one on the opposite bank. One of them said to the man clothed in linen, who was above the waters of the river [i.e. an angel], "How long will it be before these astonishing things are fulfilled?" The man clothed in linen, who was above the waters of the river, lifted his right hand and his left hand toward heaven, and I heard him swear by him who lives forever, saying, "It will be for a time, times and half a time. When the power of the holy people has been finally broken, all these things will be completed. From the time that the daily sacrifice is abolished and the abomination that causes desolation is set up, there will be 1,290 days."" (Daniel 12:1,5-7,11)
In the above passage we see a description of the time of unparalleled distress (just as Jesus described it in Mark 13:14-20, above), and we see "the abomination that causes desolation" (just as Jesus described it in Mark 13:14-20, above). Notice that in this context concerning the Great Tribulation, an angel lifted both of his hands and swore an oath (by Him who lives forever) that "It will be for a time, times and half a time." We have already seen that "a time, times and half a time" is three and a half years, and the angel swore a solemn oath with both hands lifted up to heaven that the Great Tribulation will last for three and a half years. It will not last longer than that, nor will it end sooner than that.
In order to understand what it means for the Great Tribulation to be "cut short," let's look at Mark 13:20 again:
"If the Lord had not cut short those days, no one would survive. But for the sake of the elect, whom he has chosen, he has shortened them." (Mark 13:20)
This indicates that instead of allowing the Great Tribulation to continue until no-one is left alive, God has already shortened those days by decreeing that they will last for three and a half years (exactly 1,260 days). Remember, God's plans and purposes were established long before the earth was created, and the plans of the Lord stand firm forever. His purposes will be carried out exactly as He had planned them:
"But the plans of the LORD stand firm forever, the purposes of his heart through all generations." (Psalms 33:11)
"The LORD Almighty has sworn, "Surely, as I have planned, so it will be, and as I have purposed, so it will stand. ... For the LORD Almighty has purposed, and who can thwart him? His hand is stretched out, and who can turn it back?" (Isaiah 14:24, 27)
"Remember the former things, those of long ago; I am God, and there is no other; I am God, and there is none like me. I make known the end from the beginning, from ancient times, what is still to come. I say: My purpose will stand, and I will do all that I please. From the east I summon a bird of prey; from a far-off land, a man to fulfill my purpose. What I have said, that will I bring about; what I have planned, that will I do." (Isaiah 46:9-11)
God knows "the end from the beginning, from ancient times, what is still to come" (Isaiah 46:9-11), and long ago He "cut short" the length of the Great Tribulation by decreeing that it will last for exactly 1,260 days.
The Great Tribulation will begin at the mid-point of the seven-year Tribulation period when the Antichrist breaks his treaty with Israel and desecrates the Jewish temple, and it will last for the final three and a half years of the Tribulation until Jesus returns to the earth at the Second Coming.
1 John 4: 19. We love him, because he first loved us.