The first resurrection described in Rev 20 (which includes those killed during the tribulations and the dead in Christ - all who have died since his sacrifice) is a great multitude plus, those who are alive when He returns "immediately after the tribulations" who are "caught up" as described in Thessalonians. That all happens before the marriage supper of the Lamb.
I think you asked about those souls under the alter in chapter 6. That group of martyrs was told to rest a little season longer after the fifth seal is broken. They're waiting for their brethren (more martyrs to come thru tribulations). I cannot claim to know how they got there or why. This is the throne room in heaven and John was delivered a detailed vision and it is full of difficult symbols. But I think we can assume they join the multitude who are in the first resurrection and go to the marriage supper too.
If you want to suggest there is a special rapture to get them there then the group is not just whatever we call "Christians" though. They were clearly slain for the word of God and their testimony. But even they are told to "rest" a while longer.
God's law was always present and always will be. There is no point in fooling ourselves about this.
God's law was nailed to the cross with Christ.
So there can be many ways to analyze Rev19 but you can rule out that it implies an enormous rapture event without Jesus directly mentioning it.
So where did the multitudes already in Heaven come from?
The first resurrection described in Rev 20 (which includes those killed during the tribulations and the dead in Christ - all who have died since his sacrifice) is a great multitude plus, those who are alive when He returns "immediately after the tribulations" who are "caught up" as described in Thessalonians. That all happens before the marriage supper of the Lamb.
I think you asked about those souls under the alter in chapter 6. That group of martyrs was told to rest a little season longer after the fifth seal is broken. They're waiting for their brethren (more martyrs to come thru tribulations). I cannot claim to know how they got there or why. This is the throne room in heaven and John was delivered a detailed vision and it is full of difficult symbols. But I think we can assume they join the multitude who are in the first resurrection and go to the marriage supper too.
If you want to suggest there is a special rapture to get them there then the group is not just whatever we call "Christians" though. They were clearly slain for the word of God and their testimony. But even they are told to "rest" a while longer.