The apostle Paul teaches the Rapture is not simply a resurrection from the dead or a transferral from earth to Heaven at the point of death. He tells us that those who are alive at Christ’s return will be “changed” (1 Corinthians 15:51). This change must take place before we can enter the physical presence of the Lord, “For flesh and blood cannot inherit the Kingdom of God; neither doth corruption inherit incorruption” (:50). Paul says, “We shall not all sleep” (:51). The word “sleep” is used to symbolise physical death and the bodily condition in the grave; [The Scriptures do not teach soul-sleep, but they do describe the body as being asleep in the grave.] The fact that we “shall not all sleep” means that the Rapture must be a special event that will usher both the dead and the living in Christ into His presence.
At present our spirit/soul is saved, our minds are being renewed daily (Ephesians 4:23, Romans 12:2), but the body/flesh must await the transformation from corruption into incorruption, from mortality into immortality. This is probably what Paul was referring to in Romans 8:18-21, “For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us. For the earnest expectation of the creature waiteth for the manifestation of the sons of God. For the creature was made subject to vanity, not willingly, but by reason of him who hath subjected the same in hope, because the creature itself also shall be delivered from the bondage of corruption into the glorious liberty of the children of God”. then he adds in verse 22-23 “For we know that the whole creation groaneth and travaileth in pain together until now. And not only they, but ourselves also, which have the firstfruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, the redemption of our body.” The final act of God’s redemptive plan in our lives (though we do have a guarantee of this in the Holy Spirit) is the restoration of the body to the condition it was before the Fall, but with the added aspect of literal eternal life.
Due to the Fall man was alienated from God and needed to be born again through the blood of Christ. Yet the Scriptures teach us that the flesh part of man is still in a state of corruption, that is, it can still fall into sin, it decays, and eventually dies. The flesh is also described as being “weak” (Matthew 26:41), and that in it “dwelleth no good thing” (Romans 7:14). For this reason the apostle Paul exclaims, “O wretched man that I am! Who shall deliver me from the body of this death?” (Romans 7:24)
Through the transforming power of the Lord Jesus Christ we shall be “changed” (1 Corinthians 15:52). Changed from having bodies capable of decay, sickness, pain, and death, into having bodies that will never be subject disease, weakness, or death. Our physical bodies will be made immortal (:53). In this verse Paul describes the process as putting on of immortality, therefore it is something that our bodies do not yet possess. This is so that we can, as a whole being made up of spirit, soul, and body (1 Thessalonians 5:23, “And the very God of peace sanctify you wholly; and I pray God your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ”), be made fit for Heaven and for what God has made ready for us, “As it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love Him” (1 Corinthians 2:9, Isaiah 64:4).
This transformation cannot take place until the Lord Himself returns, then, “in the twinkling of an eye” (1 Corinthians 15:52) “we shall be made like Him, for we shall see Him as He is” (1 John 3:2). The power of death will be broken forever over our flesh. Those alive at the coming of the Lord Jesus Christ will never experience physical death or the grave, but will ascend into the presence of Christ. “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. O death, where is thy sting? O grave, where is thy victory? The sting of death is sin; and the strength of sin is the law” (1 Corinthians 15:54-56). The apostle John says that we do not have this immortality of the body yet even though we are saved through Christ, “Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when He shall appear, we shall be like Him; for we shall see Him as He is” (1 John 3:2). Then we will be given a body “fashioned like unto His glorious body” (Philippians 3:21).
Knowing all of this should make us conscious of at least two things:  Since our bodies are going to be transformed when we see Christ at the Rapture, we should be faithful to the Lord and watch carefully that we are not overtaken by sin, for “every man that hath this hope in him purifieth himself, even as He is pure” (1 John 3:3). The flesh has the ability to pull the spirit down, so that the sins in the flesh become sin in the spirit resulting in damnation for both body and spirit, “Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God” (2 Corinthians 7:1).  As we approach we approach the end of all things and we see many becoming discouraged, we should “comfort one another with these words” (1 Thessalonians 4:18). To many the Rapture puts fear into their hearts because they know they will see Jesus, but we should encourage both ourselves and others not to fear but to look with joy in our hearts for His return, “Brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto Him, that ye be not soon, shaken in mind, or be troubled …” (2 Thessalonians 2:1).