So I think you and I disagree as to the identity of this great multitude. I would suggest that these are the raptured church - rescued just before God begins His judgments. And I have a question: why do you think these are martyrs? I don't see anything in the context to support that conclusion.
Yes, we disagree. I have highlighted what I see as the most reasonable explanation for the multitude.
Revelation 6:9-11
9 When He opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the testimony which they held. 10 And they cried with a loud voice, saying, “How long, O Lord, holy and true, until You judge and avenge our blood on those who dwell on the earth?” 11 Then a
white robe was given to each of them; and it was said to them that they should rest a little while longer, until both the number of their fellow servants and their brethren, who would be killed as they were, was completed.
Revelation 7:9-17
9 After these things I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the throne and before the Lamb,
clothed with white robes, with palm branches in their hands, 10 and crying out with a loud voice, saying, “Salvation belongs to our God who sits on the throne, and to the Lamb!” 11 All the angels stood around the throne and the elders and the four living creatures, and fell on their faces before the throne and worshiped God, 12 saying:
“Amen! Blessing and glory and wisdom,
Thanksgiving and honor and power and might,
Be to our God forever and ever.
Amen.”
13 Then one of the elders answered, saying to me, “Who are
these arrayed in white robes, and where did they come from?”
14 And I said to him, “Sir, you know.”
So he said to me, “These are the ones who come out of the great tribulation, and washed their robes and made them white in the blood of the Lamb. 15 Therefore they are before the throne of God, and serve Him day and night in His temple. And He who sits on the throne will dwell among them. 16 They shall neither hunger anymore nor thirst anymore; the sun shall not strike them, nor any heat; 17 for the Lamb who is in the midst of the throne will shepherd them and lead them to living fountains of waters. And God will wipe away every tear from their eyes.”
The white robed martyrs are introduced in chapter 6, and it makes sense that they are the same people (in a greater number) in chapter 7.
These who come out of the great tribulation are comforted from experiencing hunger, thirst, sun strike, heat, and tears. That seems more likely to apply to a martyr than a person who is translated without experiencing death.
The 144,000 sealed Israelite believers are sealed so they can survive the judgments coming on the earth and be protected (Revelation 7:3). The great multitude doesn't seem to survive, but they are comforted. Compare that to Revelation 14:12-13.
Can you see there's a big difference between your belief and mine? I believe most of the Church is martyred in the great tribulation but that a few will survive and be gathered when Jesus returns after the wrath is poured on the wicked. Even if you believe in a sixth seal rapture, that's not a post-Tribulation rapture the way I define would define tribulation. The seventh seal is the seven trumpets, and I think the seven bowls happen at the same time as the seven trumpets (I can see a potential relationship). If Christians were going to be translated, why would the 144,000 be left to deal with the trumpets and bowls? The 144,000 are presented as people who follow the Lamb wherever He goes (Revelation 14:4-5), without fault. Since the 144,000 aren't translated, God is able to protect His own from His wrath. (See Revelation 12:13-16.)
Sir, I urge you to consider the possibility of being martyred in the Tribulation. 144,000 is not a lot of people and no one can anticipate being one of them. Being prepared for the possibility could make you much stronger to endure in your faith in the Tribulation.
