4:13 fall asleep: This is a metaphor for dying. Though Paul had taught the Thessalonians about Christ's return when he was there, apparently Timothy had encountered further questions on the subject, possibly arising from the death of some of the new converts. In answer to these questions, Paul stated that he wanted them to be informed, and also to be comforted by the hope of seeing their loved ones again. This was a hope their pagan neighbors did not have.
4:14 This hope (v. 13) for the dead Christians was as certain as the fact of the death and resurrection of Christ. Paul says that God will bring with Him those who sleep in Jesus. Some have inferred from this statement that departed Christians are unconscious until the Second Coming. But the Bible indicates that to be absent from our present body is to be present with the Lord Jesus (5:10; 2 Cor. 5:8; Phil. 1:23). Accordingly when a Christian dies, it is the body that sleeps; the soul goes to heaven.
4:15 Paul believed that Christ could come in his lifetime, and so did the Thessalonians (1:10). precede those who are asleep: Evidently the Thessalonians were concerned that believers who had died would miss the glory associated with the Second Coming. Paul answers their questions by affirming that actually those who were dead would go before (v. 16) those living on earth.
4:16 Accompanying the descent of Christ from heaven will be the voice of an archangel, perhaps Michael, who is portrayed as the leader of the army of God (Dan. 10:13, 21; Jude 9; Rev. 12:7-9). The archangel's voice will be one of triumph because of the great victory at the coming of Christ, culminating thousands of years of spiritual conflict with Satan. The final signal will be the trumpet of God. The three elements consisting of the shout of the Lord Himself, the voice of an archangel, and the trumpet of God will perhaps be separate events occurring in rapid succession. The answer to the question as to how the dead can be raised when the remains of their bodies are in some cases totally scattered is not a problem for a super-natural God who created the world. Clearly the resurrection will be a physical resurrection in which bodily existence will be restored, as confirmed in 1 Cor. 15:51-53. The resurrected bodies of Christians will be like that of Christ (1 John 3:2), incorruptible and immortal, and yet they will be bodies of flesh and bone (Luke 24:39, 40; John 20:20, 25, 27). They all will be recognizable, as was the resurrected body of Christ.
4:17 Living Christians will be caught up together with the other believers in the clouds to meet the Lord in the air. (The English word rapture comes from the Latin verb meaning caught up). In the clouds probably refers to the atmospheric clouds that also will attend the Second Coming (Rev. 1:7), or it may be the resurrected multitudes who are referred to as a cloud (Heb. 12:1). In the Bible, the Lord is often accompanied by clouds, signifying His glory (Psm. 68:4, 97:2). The important result is that we shall always be with the Lord.
4:18 The wonderful truth described (vv. 13-17) is to be comfort to the Thessalonians and to all Christians. They had mistakenly thought that only those who were alive at the time of the coming of Christ would witness and share in the glory of it. The fact is that Christians who have died will be raised first and so go before the living to the gathering in the sky. Observe that Paul expects a practical, immediate response to this great doctrinal teaching of the Second Coming. The Thessalonians should remind one another of this truth as a source of comfort in the face of death. The sentence is in the present tense, indicating that it should be a constant comfort to us to think each day that the Lord may come.
[THE NKJV STUDY BIBLE Second Edition].
JESUS IS LORD.