4:13-18 We do not wish you to be ignorant, brothers, about those who are asleep, because we do not wish you to sorrow as the rest of people do because they have no hope. For if we believe that Jesus died and rose again, so also we can be sure that God will bring with him those who have fallen asleep through Jesus. For we tell you this, not by our own authority but by the word of the Lord, that we who are alive, who survive until the coming of the Lord, will certainly not take precedence over those who have fallen asleep. For the Lord himself will descend from heaven, with a shout of command, with the voice of an archangel and with the trumpet of God; and the dead who are in Christ will rise first, and then we who are alive, who survive, will be caught up by the clouds together with them to meet the Lord in the air. And so we shall be always with the Lord. So then encourage one another with these words.
The idea of the Second Coming had brought another problem to the people of Thessalonica. They were expecting it very soon; they fully expected to be themselves alive when it came but they were worried about those Christians who had died. They could not be sure that those who had already died would share the glory of that day which was so soon to come. Paul's answer is that there will be one glory for those who have died and those who survive.
He tells them that they must not sorrow as those who have no hope. In face of death the pagan world stood in despair. They met it with grim resignation and bleak hopelessness. Aeschylus wrote, "Once a man dies there is no resurrection." Theocritus wrote, "There is hope for those who are alive, but those who have died are without hope." Catullus wrote, "When once our brief light sets, there is one perpetual night through which we must sleep." On their tombstones grim epitaphs were carved. "I was not; I became; I am not; I care not." One of the most pathetic papyrus letters that has come down to us is a letter of sympathy which runs like this. "Irene to Taonnophris and Philo, good comfort. I was as sorry and wept over the departed one as I wept for Didymas. And all things whatsoever were fitting, I did, and all mine, Epaphroditus and Thermouthion and Philion and Apollonius and Plantas. But nevertheless against such things one can do nothing. Therefore comfort ye one another."
Paul lays down a great principle. The man who has lived and died in Christ is still in Christ even in death and will rise in him. Between Christ and the man who loves him there is a relationship which nothing can break, a relationship which overpasses death. Because Christ died and rose again, so the man who is one with Christ will rise again.
The picture Paul draws of the day when Christ will come is poetry, an attempt to describe what is indescribable. At the Second Coming Christ will descend from heaven to earth. He will utter the word of command and thereupon the voice of an archangel and the trumpet of God will waken the dead, then the dead and the living alike will be caught up in the chariots of the clouds to meet Christ; and thereafter they will be forever with their Lord. We are not meant to take with crude and insensitive literalism what is a seer's vision. It is not the details which are important. What is important is that in life and in death the Christian is in Christ and that is a union which nothing can break.
-Barclay's Daily Study Bible (NT)