Why can't the dead in Christ explain them? After all, great tribulation precedes what is recorded in Revelation 19. Then look what the following records.
Revelation 7:9 After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;
Revelation 7:13 And one of the elders answered, saying unto me, What are these which are arrayed in white robes? and whence came they?
14 And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.
Initially all of these were physically alive at some point. Then because of great tribulation they lost their lives, thus are then in heaven in a disembodied state awaiting the resurrection of their bodies. These would be among those that rise first. These are not meaning Pretribbers who allegedly came out of great tribulation by being raptured out of it. These are martyrs. Pretribbers are not mayrters if they are allegedly raptured out of great tribulation. That hardly fits the definition of a martyr.