Explanation of Text:1Thess 4:15- 16 The Lord Descends from Heaven.

1Th 4:15  For this we declare to you on the Lord's own authority--that we who are alive and continue on earth until the Coming of the Lord, shall certainly not forestall those who shall have previously passed away. 
1Th 4:16  For the Lord Himself will come down from Heaven with a loud word of command, and with an archangel's voice and the trumpet of God, and the dead in Christ will rise first. 

Notes : 

- we declare to you on the Lord's own authority    [en logoi Kuriou]

It seems here that that he, Paul was speaking by direct Revelation. 

Cp. 1Co 11:23  For it was from the Lord that I received the facts which, in turn, I handed on to you; how that the Lord Jesus, on the night He was to be betrayed, took some bread, 

It could have been a point in the Lord's Teaching which we do not have written down in the Gospels.

- that we who are alive and continue on earth until the Coming of the Lord,

This refers to Christians still living when the Lord comes.

- shall certainly not forestall those who shall have previously passed away. 

i.e. They shall not precede, anticipate or go before those who have passed away.

KJV prevent from (praevenio) = to precede.

" The meaning here is, " that they who wouldstill be alive at the Coming oftheLord Jesus, would not be "changed" and received into Glory before those who were in their graves were raised up. It was to correct the notion that those still alive  at His Coming somehow had precedence over those who have died.

1Th 4:16  For the Lord Himself will come down from Heaven with a loud word of command, and with an archangel's voice and the trumpet of God, and the dead in Christ will rise first. 

- the dead in Christ shall be raised first.

- For the Lord Himself will come down from Heaven with a loud word of command, cp. Acts 1:11
 with a Loud word of Command. WNT with a Shout [en keleusmati] from keleuo = to order or command ( a Miliatry Term.) Christ will return as a Mighty Warrior and Conqueror. Aaamen!
with an archangel's voice  [ en phonei arch-aggelou]
 This will be Michael the Archangel. Jude 1:9


with the trumpet of God  [ en salpiggi theou] 1Cor 15 :52 cp  Exodus 19:16; and Ps. 47:5 NUmbers 10:2,10.
and the dead in Christ will rise first, 
They will rise before those who are still living "are caught up."
Ps 50 :1-5
Psa 50:1  A Psalm of Asaph. The mighty God, Jehovah, has spoken, and called the earth from the rising of the sun to its going down.
Psa 50:2  Out of Zion, the perfection of beauty, God has shone.
Psa 50:3  Our God comes, and He is not silent; a fire shall devour before Him, and it shall be very stormy all around Him.
Psa 50:4  He shall call to the heavens from above, and to the earth, so that He may judge His people. 
Psa 50:5  Gather My saints to Me; and those who cut My covenant by sacrifice. 

Psa 50:6  And the heavens shall declare His righteousness; for God Himself is judge. Selah.

Mat 24:31  And He shall send His angels with a great sound of a trumpet, and they shall gather His elect from the four winds, from one end of the heavens to the other. 

1Co 15:51  Behold, I speak a mystery to you; we shall not all fall asleep, but we shall all be changed; 

1Co 15:52  in a moment, in a glance of an eye, at the last trumpet. For a trumpet shall sound, and the dead shall be raised incorruptible, and we shall all be changed. 

1Th 4:17  Then we who are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air. And so we shall ever be with the Lord.