What does 1 Corinthians 15 teach about the change in a moment?
First Corinthians 15 teaches that at the last trumpet, in a single instant, the bodies of the dead in Christ will be raised and the bodies of the living will be transformed, so that what was corruptible and mortal becomes incorruptible and immortal, and death is swallowed up in victory.
First Corinthians 15:51 to 54 declares a mystery: we shall not all sleep, but we shall all be changed. This change happens in a moment, in the twinkling of an eye, at the sounding of the last trump. The trumpet is not symbolic but a specific, literal trumpet marked by its order in the sequence of trumpets described in Revelation, and it is tied to the finishing of the mystery of God spoken of in Revelation 10:7, when the seventh angel begins to sound.
This change described in verses 42 to 44 is the resurrection of the body. What is sown in corruption is raised in incorruption; what is sown in dishonour is raised in glory; what is sown in weakness is raised in power; what is sown a natural body is raised a spiritual body. The corruptible body must put on incorruption, and the mortal body must put on immortality, and when that happens, death is swallowed up in victory, just as it is written.
This moment of change involves both those who have already died and those who are still alive. The souls of the dead in Christ are already in heaven, but their bodies remain in the earth until this moment. At the sounding of the trumpet, their bodies will rise from the grave and be changed into bodies like the glorious body of Christ, and Jesus will bring their souls back to occupy those changed bodies. They shall rise first, and then those who are alive at the coming of the Lord will have their own bodies changed in that same instant, and together they will meet Him in the air.
John 5:27 to 29 confirms that the hour is coming when all who are in the graves shall hear the voice of the Son of man and come forth, some to the resurrection of life. So the change in a moment spoken of in First Corinthians 15 is this sudden, simultaneous transformation of the dead and the living into incorruptible, immortal, spiritual bodies at the last trump.
The scriptures
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.
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 hath given him authority to execute judgment also, because he is the Son of man. 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.
But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.
And I saw the seven angels which stood before God; and to them were given seven trumpets.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.