The rest of the dead, those who have also lived and died in TIME will not be resurrected to life until the last trumpet sounds in the same hour that is coming when all in the graves will be physically resurrected to everlasting life, or condemnation. This is a depiction of the one and only physical resurrection of every human body in the graves hearing the voice of Christ and coming forth for resurrection life, or resurrection of damnation that shall come on the last day of this age of TIME.
John 5:28-29 (KJV) Marvel not at this: for the hour is coming, in the which all that are in the graves shall hear his voice, And shall come forth; they that have done good, unto the resurrection of life; and they that have done evil, unto the resurrection of damnation.
Paul spoke not only of the bodily resurrection that shall be in the hour that is coming, but also of the spiritual or first resurrection man must have part of in TIME. Paul writes with confidence, knowing that while he lived in his body destined to die he was not with the Lord in heaven. Paul found comfort in the knowledge that when he physically died he would be present with the Lord in heaven. Which is why Paul writes in death there will be great gain, for physical death could not prevent him from being with Christ which is far better.
2 Corinthians 5:6-8 (KJV) Therefore we are always confident, knowing that, whilst we are at home in the body, we are absent from the Lord: (For we walk by faith, not by sight:) We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.
Philippians 1:21-23 (KJV) For to me to live is Christ, and to die is gain. But if I live in the flesh, this is the fruit of my labour: yet what I shall choose I wot not. For I am in a strait betwixt two, having a desire to depart, and to be with Christ; which is far better:
Christ, since His resurrection became the firstfruits of them that had already died in faith. Though some faithful saints had already physically died before the advent of Christ, since they died in faith they were spiritually alive in Him, and through His Spirit ascended with Christ to heaven. As spiritual bodies, Christ descended into the place of the faithful physically dead (grave, Abraham's bosom) and freed those faithful saints who were captive in the grave. (see the parable of Lazurus & the rich man)
1 Corinthians 15:20-22 (KJV) But now is Christ risen from the dead, and become the firstfruits of them that slept. For since by man came death, by man came also the resurrection of the dead. For as in Adam all die, even so in Christ shall all be made alive.
Ephesians 4:8-10 (KJV) Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men. (Now that he ascended, what is it but that he also descended first into the lower parts of the earth? He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
Paul shows those who had already died in faith with Christ the firstfruits, were of the first resurrection. When Christ appears the second time at the end Paul shows the faithful saints being resurrected to immortality and incorruptible physical bodies fit for life in the next age on the new earth. But until that time He must reign till all enemies are put under His feet.
1 Corinthians 15:23-25 (KJV) But every man in his own order: Christ the firstfruits; afterward they that Christ's at his coming. Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power. For he must reign, till he hath put all enemies under his feet.
Answering the question of how the dead are raised up, Paul says the dead will be made alive, but that which is sown in the earth at death will not be the body raised to life. The bodies raised to life when the last trump sounds will change from mortal to immortal and corruptible to incorruptible physical bodies. But when the physical body of saints die, the body that shall be is NOT physical, but is a spiritual body, a celestial/heavenly body. The natural body will be raised in incorruption and immortal when the last trump sounds, but also raised with Christ, the firstfruits, them who died, and now all who physically die in Christ, who are raised when our natural/physical body dies, a spiritual body, because there is both a natural body and there is a spiritual body.
1 Corinthians 15:35-38 (KJV) But some man will say, How are the dead raised up? and with what body do they come? Thou fool, that which thou sowest is not quickened, except it die: And that which thou sowest, thou sowest not that body that shall be, but bare grain, it may chance of wheat, or of some other grain: But God giveth it a body as it hath pleased him, and to every seed his own body.
1 Corinthians 15:40 (KJV) There are also celestial bodies, and bodies terrestrial: but the glory of the celestial is one, and the glory of the terrestrial is another.
1 Corinthians 15:42-44 (KJV) So also is the resurrection of the dead. It is sown in corruption; it is raised in incorruption: It is sown in dishonour; it is raised in glory: it is sown in weakness; it is raised in power: It is sown a natural body; it is raised a spiritual body. There is a natural body, and there is a spiritual body.
Paul has already said that when the body of believers is dead, we are present with the Lord. Now Paul shows us how we are present with the Lord in heaven when we physically die in Him. In death believers shall be like the heavenly bodies (celestial), who, as spiritual body bear the image of the Lord from heaven, heavenly bodies. That's why Christ tells us in the resurrection we shall be as the angels of God in heaven, spiritual beings, because God is not the God of the dead, but of the living. This is why Paul writes that flesh and blood cannot inherit the Kingdom of God (in heaven), neither does corruption (mortal & corruptible physical flesh) inherit the Kingdom of God on the new earth.
1 Corinthians 15:46-50 (KJV) Howbeit that was not first which is spiritual, but that which is natural; and afterward that which is spiritual. The first man is of the earth, earthy: the second man is the Lord from heaven. As is the earthy, such are they also that are earthy: and as is the heavenly, such are they also that are heavenly. And as we have borne the image of the earthy, we shall also bear the image of the heavenly. Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption.
Mark 12:23-26 (KJV) In the resurrection therefore, when they shall rise, whose wife shall she be of them? for the seven had her to wife. And Jesus answering said unto them, Do ye not therefore err, because ye know not the scriptures, neither the power of God? For when they shall rise from the dead, they neither marry, nor are given in marriage; but are as the angels which are in heaven. And as touching the dead, that they rise: have ye not read in the book of Moses, how in the bush God spake unto him, saying, I am the God of Abraham, and the God of Isaac, and the God of Jacob?
Mark 12:27 (KJV) He is not the God of the dead, but the God of the living: ye therefore do greatly err.