1 Corinthians 15:12 (KJV) Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?
As we can see there was a question about how a mortal body of flesh (living souls) can be resurrected from the dead. Paul explains how man's living soul that dies in Christ (believers) is quickened (made alive) after death. Because Christ gives us assurance that physical death cannot kill our soul, only our body of flesh dies and returns to dust from which it came (Mt. 10:28).
Paul tells us that just as Christ arose from the dead, living on after His flesh was dead and buried, so too, we who die in Christ shall also continue to be living souls when we die. But when man dies, we are not bodily resurrected in three days as Christ was. That will not happen until the last day of this age when the seventh trumpet sounds, then our mortal bodies will be changed from mortal to immortal and corruptible to incorruptible. So, how can the life we receive when we have been born again be eternal, as Christ says, if death of our mortal flesh means complete death of our living soul? Christ would not have told us our life IN HIM is eternal if death of our mortal body is also death of our spirit that together with body of flesh makes us living souls!
Paul, in this passage of Scripture goes into great detail explaining how death of our mortal natural body transitions after we cease to be physically alive. The body sown after death is not the same body that shall live on eternally after physical death. That natural body will be changed. God will give it (body) that which pleases Him, that shall not be complete living soul, but changed into a celestial/heavenly body that is spiritual as is the Lord from heaven. Though believers are in life natural body, after death it (natural body) is raised a spiritual body. Because Paul tells us there is both a natural body and there is a spiritual body. The natural body comes first through natural man, made a living soul. After death that which was natural body is afterward spiritual, because in life we have borne the image of the earthy natural man of flesh & blood, and after death we will be the likeness of Christ in heaven. Since the life we have in Christ when we have been born again is eternal, we must be raised a spiritual body after we die, to as be the angels of God, spirit without flesh & blood. We cannot inherit eternal life in heaven a natural body because flesh and blood cannot inherit the Kingdom of God.
Lastly, after explaining how we continue to be the spiritual body of Christ in heaven after we physically die, Paul also assures us how and when our mortal body of flesh & blood shall also be changed from mortal to immortal and corruptible to incorruptible shall be alive again through our living spirit/soul that shall be with Christ when the last trumpet sounds.
1 Corinthians 15:35-45 (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. All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds. There are also celestial bodies, and bodies terrestrial: but the glory of the celestial is one, and the glory of the terrestrial is another. There is one glory of the sun, and another glory of the moon, and another glory of the stars: for one star differeth from another star in glory. 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. And so it is written, The first man Adam was made a living soul; the last Adam was made a quickening spirit.
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.
1 Corinthians 15:51-54 (KJV) Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality. So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.