Paul is referring to the rapture, which speaks to the 1st advent of Christ where Christians believe they will be taken from the earth bodily by Jesus, before the tribulation begins (Rev 3:10) and before the thousand year reign of Christ on earth begins. The change refers to the body becoming immortal without blood, Paul refers to this as corruption.
1 Thessalonians 4:13–17
13 But I would not have you to be ignorant, brethren, concerning them which are asleep, that ye sorrow not, even as others which have no hope.
14 For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him.
15 For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.
16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:
17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
1 Corinthians 15:50-52
50 Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption.
51 Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed,
52 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.
Jesus is the “first” to experience this transition, the rapture is also referred to as the “First Advent” of Christ, Jesus “first” coming, the 2nd advent would refer to the battle of Armageddon.
1 Thessalonians 4:13-17; 1 Corinthians. 15:50-55; Matthew 24:40-42; Luke 17:34-36 Matthew 24:36-51; Mark 13:32-37.
In this context Jesus is also referred to as the “first begotten of the dead”
Revelation 1:5
“From Jesus Christ, who is the faithful and true witness, and the first begotten of the dead”
Jesus being the “first” to be resurrected, death is superseded by the rapture.
The application of the rapture is for a small group of people on earth, in a small window of time, that will only be active for the space of a twinkling of an eye, which is to say, it will apply for a fraction of a second, a one off experience if you please.
At the final judgment, all people must stand before God in the manner they were created, in your earth suit so to speak. This is manifested at the Great White Throne Judgment where God calls for all the bodies throughout time, to be reconstituted from wherever they died at the time, regardless if they were devoured, disintegrated, burned up or however the body met its doom.
Once the bodies are reconstituted, the persons spirit is reconciled with their body just like the rapture for those who went to Heaven. At this point the judgement takes place.
Revelation 20:11–15
11 And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them.
12 And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.
13 And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.
14 And death and hell were cast into the lake of fire. This is the second death.
15 And whosoever was not found written in the book of life was cast into the lake of fire.
The point here is that the significance of Jesus’ body being resurrected gives predicate to us being resurrected as well. He is the first to go through this experience which was in part was to show us, to reveal to us, what will happen to us, as with the disciples encounter with Jesus upon His transition.
What is spiritual about this event is how God chooses to accomplish this and the faith of those who are saved, enabling them be raptured in the first place. One very telling thing about how God operates, is that God does what He has done in the past to confirm that what you are seeing or experiencing is Him.
The principles for the rapture is first seen with Elijah and the dry bones.
Ezekiel 37:1-14
1 The hand of the Lord was upon me, and carried me out in the spirit of the Lord, and set me down in the midst of the valley which was full of bones,
2 And caused me to pass by them round about: and, behold, there were very many in the open valley; and, lo, they were very dry.
3 And he said unto me, Son of man, can these bones live? And I answered, O Lord God, thou knowest.
4 Again he said unto me, Prophesy upon these bones, and say unto them, O ye dry bones, hear the word of the Lord.
5 Thus saith the Lord God unto these bones; Behold, I will cause breath to enter into you, and ye shall live:
6 And I will lay sinews upon you, and will bring up flesh upon you, and cover you with skin, and put breath in you, and ye shall live; and ye shall know that I am the Lord.
7 So I prophesied as I was commanded: and as I prophesied, there was a noise, and behold a shaking, and the bones came together, bone to his bone.
8 And when I beheld, lo, the sinews and the flesh came up upon them, and the skin covered them above: but there was no breath in them.
9 Then said he unto me, Prophesy unto the wind, prophesy, son of man, and say to the wind, Thus saith the Lord God; Come from the four winds, O breath, and breathe upon these slain, that they may live.
10 So I prophesied as he commanded me, and the breath came into them, and they lived, and stood up upon their feet, an exceeding great army.
11 Then he said unto me, Son of man, these bones are the whole house of Israel: behold, they say, Our bones are dried, and our hope is lost: we are cut off for our parts.
12 Therefore prophesy and say unto them, Thus saith the Lord God; Behold, O my people, I will open your graves, and cause you to come up out of your graves, and bring you into the land of Israel.
13 And ye shall know that I am the Lord, when I have opened your graves, O my people, and brought you up out of your graves,
14 And shall put my spirit in you, and ye shall live, and I shall place you in your own land: then shall ye know that I the Lord have spoken it, and performed it, saith the Lord.