Paul next turned to another subject on which his readers needed instruction in view of their newness in Christ (cf. 1 Thessalonians 3:10). He outlined the immediate hope of his readers. He did this to explain that those of their number who had died, or would die in Christ, would share in His glory with those who were living when He returned. This pericope deals with the relation of their dead brethren to Christ"s return. [source][source][source]
"It would seem that some, at least, of the Thessalonians had understood him to say that all who believed would see the Parousia; but now some believers had died and they had begun to wonder about them." [1][source]
The time of the Rapture has been a matter of disagreement among conservative interpreters. Some believe it will take place before the Tribulation (pretribulationists). Others believe that it will take place after the Tribulation (posttribulationists). Others conclude that it will take place during the Tribulation (midtribulationists). Still others hold that the Lord will catch away only some Christians, not all (partial rapturists). What does 1 Thessalonians 4:13-18 reveal about the time of the Rapture? How do advocates of the various schools of interpretation cited interpret these verses? 1 Thessalonians 4 , 5 are "probably the most important passages dealing with the Rapture." [2] Other key New Testament passages that deal with the Rapture are John 14:1-3 and 1 Corinthians 15:51-53. [source][source][source]
I believe it is fair to say that more pretribulationists base their belief that the Rapture will occur before the Tribulation on1Thessalonians4than on any other one passage of Scripture. This passage also contains more detail about the Rapture than any other one. It has major significance. All conservative interpreters agree that the translation of living Christians and the resurrection of dead Christians will take place at the same time. On this issue there is agreement regardless of when the Rapture will occur in relation to the Tribulation. [source][source][source]