You are skipping over the words "together with them" in verse 17.
The believers that remained alive are not caught up by themselves.
They are caught up together with the believers that were raised from the dead.
The following translation makes the order of the events more clear:
"According to the Lord’s word, we tell you that we who are still alive, who are left until the coming of the Lord, will certainly not precede those who have fallen asleep. For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever" (1 Thess.15-17).
The Christians who have already died physically will be with the Lord when He descends from heaven and they will be raised in new bodies first. Then after that the living saints will meet them in the air.
Besides that, can you tell me what Paul was referring to when he used the words "naked" and "unclothed" in the following verses?:
"For we know that if our earthly house of this tabernacle were dissolved, we have a building of God, an house not made with hands, eternal in the heavens. For in this we groan, earnestly desiring to be clothed upon with our house which is from heaven: If so be that being clothed we shall not be found naked. For we that are in this tabernacle do groan, being burdened: not for that we would be unclothed, but clothed upon, that mortality might be swallowed up of life" (1 Cor.5:1-4).
Thanks!