So getting back to your scripture reference....
Let's take it from a more reliable translation in modern English (NASB).....we'll break it up....
"13 We do not want you to be uninformed, brothers, concerning those who are asleep, so that you will not grieve like the rest, who have no hope."
So, clearly those who are "asleep" (Gk "koimaō") are those who have died. There is no need to overly "grieve" because of the "hope" of the resurrection of the dead.
"14 Since we believe that Jesus died and rose again, in the same way God will bring with Him those who have fallen asleep through Jesus."
Believing that Jesus died and rose again, we see that those who have "fallen asleep through Jesus" i.e. those who were endowed with "the heavenly hope" will experience the same death and resurrection as he did. What was that? Peter answers...(1 Peter 3:18)
"For Christ also died for sins once for all. . . .having been put to death in the flesh, but made alive in the spirit". These were to receive a spiritual resurrection like Jesus did in order to enter heaven. As mentioned, this was to take place first, when Jesus was to take up his kingship at the time of his promised return. When was that to be?
"15 For we say this to you by a revelation from the Lord: We who are still alive at the Lord’s coming will certainly have no advantage over those who have fallen asleep."
So those who have been "asleep" in their graves a very long time, will be resurrected first. That will be before the gathering of his remaining ones still on earth when he comes as judge.
None of the elect had gone to heaven before Jesus returned, because Jesus had to wait for certain events to take place on earth, and so they did too. (Psalm 110:1-2)
The Lord's "coming" I believe is misunderstood because the word used in Matthew 24:3 in Greek means "presence" not "coming". So Jesus "presence" was tied up with the "sign" he gave at Matthew 24:3-14. All these things were to take place at his return, so Jesus is already here, overseeing the work that he assigned to his disciples in this "time of the end". (Matthew 28:19-20) His "presence" was the beginning of "the last days".....and his "coming" as judge is a completely separate event, that was to take place at the end.
"16 For the Lord Himself will descend from heaven with a shout, with the archangel’s voice, and with the trumpet of God, and the dead in Christ will rise first."
Do you see the chain of events and in the order in which they take place? Christ was to "descend from heaven" with an "Archangel's voice" and call those of the "elect" who had died faithful down through history, out of their graves....these were to "rise first"....and they began to be resurrected when Christ first made his "presence" apparent. He gave a "sign" because his return was not observable by the world.
Those who believe that all the faithful went straight to heaven upon their death, are mistaken. All 'slept' in their graves awaiting the time when Jesus would awaken them. They knew it was in the future but they did not know when.
"17 Then we who are still alive will be caught up together with them in the clouds to meet the Lord in the air and so we will always be with the Lord."
Only when the full number of the 144,000 who were still in their graves are resurrected, will Jesus gather the remaining ones who are still alive when he returns...these have no need to "sleep" but will be transformed instantly, leaving their physical bodies behind and experiencing a spiritual rebirth to join their companions in their roles as "kings and priests" over redeemed ones on earth.
"18 Therefore encourage one another with these words."
This is the hope they found encouraging.....what would be the point of them hanging around in heaven waiting for thousands of earth years to pass?
Better to sleep as if in a state of suspended animation, and be awakened when their new role was to begin. The dead are not conscious as Solomon said. (Ecclesiastes 9:5, 10)
