As an addendum to my comments above, I offer the folowing text from the Babylon book, pages 574-5:
However, disastrous things can come from above as well as from underfoot. Showing that the air or atmosphere has been affected by the pouring out of the seventh bowl of God's anger is the fact that out of heaven there descends upon disobedient men a "great hail," with every hailstone weighing 96 pounds avoirdupois. Their falling with speed adds to the de structive effect of these tremendous "hailstones." Since hailstones are congealed water, this hailstorm pic tures that Heaven would send down upon worldly man kind a barrage of hard Biblical truths. These would be God's judgment messages for delivery by his Chris tian witnesses on earth. Instead of the good news of salvation by God's kingdom, the hard, unyielding message of God's vengeance against Satan's visible organization will at the last pelt men. It will presage their destruction.
The symbolic hailstorm was not meant or expected to convert mankind at that late development of world affairs. So what was foreshown to the apostle John was that "the men blasphemed God due to the plague of hail." They did not call upon the name of Jehovah for salvation but blasphemed him because of the delivery of the judgment messages and the execution of them. (Joel 2:32; Romans 10:13) The fact that "the plague of it was unusually great" foreshows that at the last there will be an unusually great proclamation of God's vengeance by Jehovah's witnesses. —Revelation 16:21.
For the wicked ones there is no escaping from God's vengeance. In the Revelation picture, if they survived the symbolic earthquake, they would without fail be destroyed by the accurately aimed, executional hailstones from the heavens. (Job 38:22,23; Psalm 148: 7,8; Isaiah 28:2,17) The full execution of the seventh of those "seven plagues" will bring destruction to all persons on earth who bring forth the wicked fruitage of Satan's spirit. But happy will those people be who get filled with God's spirit and produce its fruit!