What does Revelation 16:21 mean?

The seventh and final bowl judgment brings not only a devastating worldwide earthquake but also a crippling hailstorm. Each hailstone weighed about 100 pounds and these falling monstrosities pummeled people.

As of this writing, the heaviest recorded hailstone recorded in the United States weighed just under two pounds. That storm fell on South Dakota in 2010. Damage from such a storm is devastating, and incredibly dangerous for any living thing caught outside. One can only imagine what injuries will occur when the seventh bowl judgment brings hailstones many times larger than anything yet seen on earth.

Isaiah 30:30 associates hailstones with God's judgment. Ezekiel 13:13 also associates hailstones with His wrath, stating, "Therefore thus says the LORD GOD: I will make a stormy wind break out in my wrath, and there shall be a deluge of rain in my anger, and great hailstones in wrath to make a full end." The seventh plague in Egypt in the time of Moses was enormous, unprecedented hail that "struck down everything that was in the field in all the land of Egypt, both man and beast" (Exodus 9:25). Nevertheless, when the storm ended, Pharaoh hardened his heart and would not release the Hebrews from their slavery in Egypt (Exodus 9:34). Like Pharaoh, people struck by the 100-pound hail in the great tribulation period will refuse to repent. Instead, they curse God because of the hail. Once again, the human heart is seen as callous and desperately wicked.