You're probably assuming this is a silly question, only movies and TV shows sometimes suggest Angels are Humans who died, but clearly that's not Biblical. But actually Revelation has two verses that seem to imply exactly that.
19:10. "And I fell at his feet to worship him. And he said unto me, See thou do it not: I am thy fellowservant, and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy."
22:8-9. "And I John saw these things, and heard them. And when I had heard and seen, I fell down to worship before the feet of the angel which shewed me these things. Then saith he unto me, See thou do it not: for I am thy fellowservant, and of thy brethren the prophets, and of them which keep the sayings of this book: worship God."
Most gloss over these just assuming they're about how Believers will be like the Angels in the Resurrection. But the exact terminology is clearly saying more then that. The word "Brethren" implies biological kinship.
Clearly not all Angels are. For one thing no Fallen Angels can be, once a Human is saved and redeemed in Jesus that can't be undone.
Also no Old Testament Angels were in my view. I believe this is referring to people who are Resurrected (truly Resurrected), and no one was Resurrected before Jesus was in 30 AD. So all Old Testament Angels are separate Creations of God, not kin to Adam.
This takes me again to Matthew 27:52-53 during it's account of the Death of Jesus on The Cross.
"And the graves were opened; and many bodies of the saints which slept arose, and came out of the graves after his resurrection, and went into the holy city, and appeared unto many."
Post-Tribulationists (and maybe also some Pre-Wrathers) and others who's Eschatology has trouble with The Resurrection of Believers not happening all at once, or who want to deny the Resurrection we are promised is a literal Bodily one at all. Need to insist that these are only a temporary Resurrection like Lazurus, not part of the True Resurrection.
I like to respond to that by saying Jesus had already done that, that wasn't a new sign anymore. This is after his Resurrection so I feel it must be in part to further show that the Resurrection has come. And then I tie it into the Doctrine of Christ's descent into Hades/Sheol (commonly called Hell).
But it is hard to prove doctrinally a detail only alluded to in one of the four Gospels. None the less I have felt lead by The Holy Spirit to view this frequently over looked detail as vital to unlocking many mysteries related to The Resurrection.
Now that I have also noticed this overlooked fact from The Book of Revelation, I feel assured more then ever my view is right. Many Old Testament saints have already been Resurrected and have become Angels.
Remember, Angel is not a zoological, or technical term. It simply means messenger. So certainly God could be using these Resurrected individuals as messengers if he wants to. And it is used sometimes of still living not yet resurrected Humans, like Jesus using it of John the Baptist quoting Malachi 3. And I agree with the view that the Angels of he seven Churches were believers in those congregations who held that as their office.
Were all Old Testament Saints Resurrected then? The wording says many, not all. And indeed I don't want to rule out any pre 30 AD bodies we know are still here un-resurrected because we have their bodies from being among the Saved. Any remaining would be Resurrected at the same time as the post-Rapture saints.
Why was Satan interested in the body of Moses in that account related in Jude's Epistle? Some want to tie that into the Two Witnesses mystery, but I view the other Witness as Enoch. I think perhaps God wanted the rising of Moses to also be a witness to the Resurrection. I've seen some theorize this passage is about Moses' Resurrection, Michael seems to be linked to the Resurrecting of Saints in Daniel 12.
The two verses from Revelation are different in the wording they use. It is unclear if they're actually the same Angel. I'm hesitant to argue that of course John wouldn't start worshiping again the same one that had already corrected him, his doing that at all doesn't seem logical to us, you'd have to be there.
The scene from Chapter 22 is immediately followed by John being given an instruction that parallels instructions given to Moses by God about the writing of The Torah in The Torah. So that has me thinking Moses could be who this is. The beginning of the Canon and the end of the Canon together.
The 22 verse is using terminology that implies an Old Testament saint. The verse in Chapter 19 sounds at first like it could be of a New Testament believer with it's terminology. But no one of The Church Age has been Resurrected yet. Maybe he's the thief who was on the Cross next to Jesus who was promised he'd be with him in Paradise?
His story is a strong Testimony of The Gospel. And he's in a unique place historically, the only Saved person known to have died after the end of the "Law and the Prophets", which "were until John (The Baptist)", but before the Birth of The Church at Pentecost. There could have been others, but he's the only Biblically documented example.
The 24 Elders are frequently by Pre-Tirbbers identified as The Church now in Heaven after The Rapture. Their proof of this is being described as individuals made "kings and priests" in 5:10. Which John says of us believers in 1:6. As a Mid-Tribber I agree with Pre-Tribbers on the uniqueness of The Church, not all saved are part of The Church. But this particular promise to Co-Reign with Christ is not among the Church specific promises.
David we know will be be a co-ruler during The Messianic Kingdom from Ezekiel 34 and 37 as a "Prince"(Nasi). He I believe is the same "Prince"(Nasi) from Ezekiel 40-48. Revelation 20 informs us that those post Rapture saints martyred for not taking The Mark or worshiping The Beast's Image will be co-ruling during The Millennium.
I agree that it's significant that the 24 Elders are not in the Old Testament visions of The Heavenly Throne Room in Isaiah and Ezekiel.
The 24 Elders have Crowns already. So they've already received rewards. The Church Age believers rewards are given after The Seventh Trumpet based on what's said in Revelation 11. So I think these also are Resurrected Old Testament believers.
Because I view Revelation 21 as clearly defining The Church/The Bride of Christ as synonymous with New Jerusalem. I also conclude that The Church isn't on Earth during The Millennium. So I must also conclude that the saints with Jesus when he returns riding on a White Horse in Revelation 19 are also those Resurrected in 30 A.D.
Jude quoting Enoch said there he would come with "Ten Thousands of his Saints". That seems like a lot to be strangely unnoticed by Secular history. Chuck Missler and Mark Easton argue that Jesus in his Resurrection was only visible to Saved individuals during those 40 days in 30 A.D.
I feel Enoch's Prophecy helps prove my point, they can't be all the Saved. The Church has far more then a mere Tens of Thousands. As a Mid-Tirbber I view the 144,000 as the bare minimum of just those alive when The Rapture happens, much less the Dead in Christ who Rise first.