What does Luke 21:26 mean?

Here, Jesus more fully describes the reaction of the people during the horrors of the tribulation. The sun, moon, and stars will dim, rage, and turn dark (Revelation 6:12–13; 8:12; 16:8–11). The seas will turn to blood and everything in it will die (Revelation 8:8; 16:3). The nations will be distressed and confused (Luke 21:25).

The people will faint with fear. They will crawl into caves, begging the stones to cover them, to hide them from the Son of Man (Revelation 6:15–16). But there will be no escape. It is time for God to judge the world for seeking authority in themselves, their own creations, and demons, instead of submitting to their Creator (Romans 1:18–23).

At this time, the "powers of the heavens will be shaken." Satan, the "god of this world" (2 Corinthians 4:4) will find his power slipping. He will hold tight to the Antichrist but fall powerless when Jesus returns "in a cloud with power and great glory" (Luke 21:27). Jesus will destroy both the physical and economical Babylon (Revelation 17—18), annihilate the Antichrist and his armies (Revelation 19:11–21), imprison Satan (Revelation 20:1–3), and take His rightful throne for a thousand years (Revelation 20:4–6).

The disciples still think Jesus is going to expel the Romans and restore Israel to independence. They don't realize that within days Jesus will hang on the cross. Even after His resurrection, they anticipate His kingdom (Acts 1:6). Jesus is telling them His followers must first face a lot of hardship, persecution, and horror. But their redemption will come (Luke 21:28).