Mt. 27: 51-53: Then, behold, the veil of the temple was torn in two from top to bottom; and the earth quaked, and the rocks were split, and the graves were opened; and many bodies of the saints who had fallen asleep were raised; and coming out of the graves after His resurrection, they went into the holy city and appeared to many.
My question is not where they WERE. I don't think they were anywhere. My question is what became of them? Christ was the first to be raised from the dead in a true resurrection (Others who were raised before him were merely resuscitated, e.g. Lazarus whom Christ brought back to life. No doubt he died again). But did the saints referred to in the verse above receive a true resurrection as did Christ? Were they, like Christ the "firstfruits" of the resurrection? Did they go to heaven at some point?
As I see it the resurrection of the saints is in three stages:
1. The firstfruits —Christ Himself, and perhaps those saints coming out of their tombs as described in the quoted verse.
2. The harvest — those who are raised when Christ comes again (the first resurrection).
3. The gleanings — those who are raised at the end of the millennium (the second resurrection)
Revelation 20:7-15
And when the thousand years are ended, ... I saw a great white throne and him who was seated on it. From his presence earth and sky fled away, and no place was found for them. And I saw the dead, great and small, standing before the throne, and books were opened. Then another book was opened, which is the book of life. And the dead were judged by what was written in the books, according to what they had done...
And if anyone’s name was not found written in the book of life, he was thrown into the lake of fire.
It seems that most people who are raised in this second resurrection (after the millenium) will be thrown into the lake of fire. But the last sentence seems to imply that there will be some whose names
will be found written in the book of life. The resurrection of those few constitute "the gleanings".
Those are my thoughts. I don't declare them as "gospel truth".