Because the Lord Himself, with a shout, with the voice of an archangel, and with a trumpet of God, will descend from heaven and the dead in Christ will rise first (1 Thessalonians 4:16).
Paul reveals to us what will happen at the rapture—the snatching away of the Church from the earth by Jesus Christ. Christ Himself will be the one coming to receive the Church. “Archangel” means the beginning angel; that is, the angel above all other angels. This angel is Michael, who also serves as the prince of Israel (Jude 9; Daniel 12:1). As the highest-ranking angel, the demons (fallen angels) are still subject to his authority (2 Peter 2:10). He will shout, clearing the way for the saints of the Church to meet Christ in the air. Then the trumpet of God will sound, calling His saints to Himself, causing the dead in Christ to rise. For those who are alive and remain at the coming of the Lord will by no means precede those who have fallen asleep—we are all going together.