I will point to what the subject is:
1st Thessalonians 4:
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.
Paul said, I do not want you to be ignorant about where are the dead. Those that do not have hope are the non believers. If your confused about the simple figure of speech that sleep means dead, read ( John 11: 11-14 ; 1 Kings 2:10-12 etc )
14 For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him.
If you believe Christ died and rose again, those who have died and believe in Christ will Christ bring with Him. Why? Because Paul just said, don't be ignorant , they rose also and are with Him already. ( Luke 23:43 )
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.
For this reason, God's word states, shall not go before ( it's what prevent means in the Greek ) those who have died, because they are already there as I ( Paul ) stated in verse 14.
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:
Paul is beating the point, those Christians rise first because of the subject verse 13 -14, because they are already there, you cant ''go before them '' ( Prevent in the Greek in verse 15 ) , because they are already there. ( 2 Corinthians 5:8 ; Ecclesiastes 12:6-7 .
You don't want to get confused by how these teaching appear in English. Don't look at the:" dead in Christ" as people who are dead as in a grave some where.
Mark 12:27 He is not the God of the dead, but the God of the living: ye therefore do greatly err.
Notice Paul mentions the Voice of the archangel and the trump of God at Christ return .
Revelation 11:
15 And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.
The seventh angel sounding is the last trump. Paul mentions this last trump in 1 Cor 15 .
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.
We, which are alive, when it is Time for Christ to return, not before, shall be gathered together with those who have passed on to be with Christ, in a great Cloud of Christians ( Hebrews 12: 1 ) . Christ is returning here, so that air is that
I would read 1 cor 15, Paul there taught what this ' in the air '' means, ( 1 Corinthians 15:51-52 " the air, breath of life body- Greek " At the last trump which we just read is the seventh the angels sounds.)
18 Wherefore comfort one another with these words.
It should be a comfort.. Paul continues with His 2nd letter, Detailing what Must happen first, before the above happens, before Christ return. Satan comes first, because he comes at the 6th trump' , as Paul makes clear in 2nd Thessalonians chapter 2.