Interestingly the term "great tribulation" is used in the Revelation from which a huge number of believers are martyred into heaven relatively early on in the tribulation. All of those believers are seen by John in heaven, so many in fact that they couldn't be numbered. It's interesting in part because these are not pre-trib believers rather they come out of "great tribulation". This indicates a huge unequaled revival will breakout early in the Tribulation bringing about a huge persecution.

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