The death of believers before the parousia was something that the Thessalonian church had not been prepared for, and a problem was thereby created in their minds on which they sought enlightenment. They seem, in fact, to have put two questions to Paul:
a. At Christ’s parousia, what will be the lot of those believers in him who have died before he comes?
b. When may the parousia be expected?
In answering the former question Paul assures them that those of their number who have died before the parousia will suffer no disadvantage when it take place; “we who are left alive until the Lord comes shall not forestall those who have fallen asleep”. On the contrary, when the Lord descends from heaven with the shout of command, the archangel’s voice and the trumpet blast, those who respond to his summons first will be the dead in Christ; when they rise at his call, brought to life with him who died and rose again, “then we who are left alive shall join them, caught up in clouds to meet the Lord in the air” (1 Thessalonians 4:14–18). This assurance is conveyed to them “by the word of the Lord”—on the authority of an utterance of Jesus himself (whether given before his death or subsequently we need not now inquire). The language and imagery are those associated with Old Testament theophanies of redemption and judgment—we may think of the trumpet blast which calls home the dispersed of Israel in Isaiah 27:13 and the clouds of heaven on which one like a son of man is brought to the Ancient of Days in Daniel 7:13—but what is here communicated in these terms is new and distinctively Christian. Because Jesus died and rose again, those who die believing in him cannot fail to rise with him; and all his people must live forever with him. F.F. Bruce
Apostle of the Heart Set Free.