The question of those still alive at the time of the end of the world has always concerned believers. Some evangelical Christians have developed a teaching on the so-called "rapture." It is based on a passage from Matthew's Gospel. Some believe in a rapture before Jesus' second coming. These teachings began in 1830 in the Plymouth Church in England from a man named John Nelson Darby. Catholic Christians simply accept Christ's explanation of those still alive at the end of the world.
(In reply, Jesus said to them:) "But of that day and hour no one knows, neither the angels of heaven, nor the Son, but the Father alone. For as it was in the days of Noah, so it will be at the coming of the Son of Man. In (those) days before the flood, they were eating and drinking, marrying and giving in marriage, up to the day that Noah entered the ark. They did not know until the flood came and carried them all away. So will it be (also) at the coming of the Son of Man. Two men will be out in the field; one will be taken, and one will be left. Two women will be grinding at the mill; one will be taken, and one will be left. Therefore, stay awake! For you do not know on which day your Lord will come."
Paul says that (1) the resurrection of the dead of the dead will precede the second coming. According to Paul, the Lord will command those who have suffered human death to rise. Only then (2) will those still living at the end of time join the resurrected dead. Both groups together (3) will be witnesses to Christ's coming.
1 Thess 4:16-18
For the Lord himself, with a word of command, with the voice of an archangel and with the trumpet of God, will come down from heaven, and the dead in Christ will rise first. Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air. Thus we shall always be with the Lord. Therefore, console one another with these words.