4:16 shout. The “shout” is a military command; the great event is described as a military assault with the great host of heaven, under the command of an (not “the”) archangel (probably Michael—compare Jude 9; Revelation 12:7-9), penetrating Satan’s domain (i.e., “the prince of the power of the air”—Ephesians 2:2; 6:12). The Lord Jesus Himself will lead the mighty army of heaven, and Satan’s hosts are powerless to stem the tide. The old “strong man” of this world—that is, the Devil—will soon be bound, and the Lord “will spoil his house” (Matthew 12:29), raising the dead and rapturing into the air all His redeemed ones, whether living or sleeping.
4:17 caught up. “Caught up” means “raptured” (Greek harpazo; the same word is used in II Corinthians 12:2,4; Acts 8:39 and Revelation 12:5). The English word “rapture” comes from the Latin raptus, meaning “seized” or “carried away.” This verse, of course, is the classic defining passage on the great doctrine of the “rapture of the saints,” caught out of this world to be forever with the Lord.
4:17 together with them. The dead in Christ will first be resurrected, their bodies once again serving as the temples of their souls and spirits, but made immortal (see I Corinthians 15:51-54). Then those saints living at the time (quite possibly many in this present generation) will likewise receive immortal, glorified bodies like that of the Lord Jesus Himself (I John 3:2; Philippians 3:20,21), and be caught up “together with them.” Then both living and dead believers, all reunited in the rapture, will together meet the Lord in the air.
4:18 comfort. “Comfort” equals “strengthen.” When we have such a blessed hope to share, it is surely reasonable that we “sorrow not, even as others which have no hope” (I Thessalonians 4:13) when our loved ones die.