When he opened the seventh seal, there was silence in heaven for about half an hour. (Revelation 8:1 NIV)
The tribulation period is going to be a time of horrible judgment for unrepentant humans. It is so bad, that when the 7th seal was opened in John’s vision, that there was silence in heaven for half an hour. The first six seals had been bad enough, but the seventh seal was so much worse.