What does “unless those days be shortened” mean (Mark 13:20)?

Jesus spent time telling His disciples about the end times in Matthew 24, Mark 13, and Luke 21. The end times, commonly called the tribulation, will witness God’s judgment on an unbelieving world. Jesus said it will be a time of unprecedented severity: “Those will be days of distress unequaled from the beginning, when God created the world, until now—and never to be equaled again” (Mark 13:19). In fact, Jesus said that “unless the Lord had shortened those days, no life would have been saved” (Mark 13:20, NASB 1995).

In Mark 13, Jesus identifies four signs leading up to the end times or the tribulation:

1. Spiritual deception (verses 5–6)
   
2. International conflict (verse 8a)
   
3. Natural disasters (verse 8b)
   
4. Persecution of Christians (verses 9, 12–13)

Then comes the worst of it: when “the abomination that causes desolation” is revealed, Jesus warned, Jews living in Jerusalem will need to “flee to the mountains” (Mark 13:14). For then will come the “days of distress” unparalleled in the history of the world (Mark 13:19). It will be the most severe time of trouble ever.

“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). With this statement Jesus alludes to both the dreadful nature of that time and the mercy of God. The plagues the befall mankind during the tribulation will be intense beyond imagination (see Revelation 6—16). If God allowed the plagues to run their course, no living being would survive.

But, in His mercy, God shortens those days. That is, He brings the tribulation to an end before humanity is destroyed. The Lord is “the compassionate and gracious God” (Exodus 34:6). In judgment, we can always find God’s mercy:

• in mercy, God spared Rahab in the judgment of Jericho
  
• in mercy, God spared Nineveh after Jonah’s preaching
  
• in mercy, God spared Zoar for Lot’s sake
  
• in mercy, God spared Noah from the flood
  

The principle found throughout Scripture is that “mercy triumphs over judgment” (James 2:13). Another is that God distinguishes His children from the wicked. As Abraham was interceding with the Lord for Sodom, he expressed confidence that God would never “kill the righteous with the wicked, treating the righteous and the wicked alike” (Genesis 18:25; cf. 2 Peter 2:9).

God will curtail the duration of the tribulation period for a specific reason: “For the sake of the elect, whom he has chosen” (Mark 13:20). The “elect” are people God has chosen in Christ—the redeemed—and it is for their sake that God shortens those terrible days. Believers in Christ receive special consideration (see Mark 13:27), and their very presence in the world will ensure the preservation of a remnant of humanity.

The apostle Paul has this warning for sinners who refuse to turn from their ways: “Because of your stubbornness and your unrepentant heart, you are storing up wrath against yourself for the day of God’s wrath, when his righteous judgment will be revealed” (Romans 2:5). God will be faithful to bring His “righteous judgment,” and He will be just as faithful to preserve His elect. “In wrath” God will “remember mercy” (Habakkuk 3:2). He will cap the catastrophes; He will shorten the days of disaster.