In addition to posts 110 and 112, even if you don’t accept any of what was said there, in Rev 8:3 it says the incense is the prayers of “all saints” in virtually every translation I’ve found. So even if one says, “the believers in God who are Christians are ‘saints’ on earth, and these are the saints in verse 4”, this distinction is not made in Rev 8:3.
So Rev 8:4 can be reasonably interpreted (even given the Protenstant insistence we are “saints” here on earth), if even that is conceded, then STILL we have “ALL saints’” (prayers) offered up to God in verse 4, which then includes (obviously) the saints in heaven. Since the saints in heaven are some of the group known as “all saints” in verse 3.
Unless one will foolishly assert that the saved believers in heaven aren’t saints!
The persons in heaven are properly called saints. If one at least agrees with that then...
...since the saints in heaven are at least part of the group of people known as “all saints” and since the saints in heaven have nothing to pray for other than other people, and the only other people they would need to pray for would be those on earth, Rev 8:3-4 still shows that at least SOME of the prayers of the saints (in verse 4) are of those saints in heaven for other people here on earth.
Q.E.D.
Our prayers may very well be eternal. The Bible says elsewhere that our tears are bottled in Heaven. We are getting a glimpse here into the ternal, and both our prayers and our tears may never cease to exist, and really can’t cease to exist to God, who is outside of time.
That argument only works if you first concede that the dead saints are still able to pray. You are making a huge assumption that cannot be supported with Scripture to support your argument.