19 But let us wait and look for the Lord's coming upon the clouds from heaven. Then shall Angelic trumpets sound; the dead in Christ shall rise first —the godly persons who are alive shall be caught up in the clouds, receiving as the reward of their labours more than human honour, inasmuch as theirs was a more than human strife; according as the Apostle Paul writes, saying, For the Lord Himself shall descend from heaven with a shout, with the voice of the Archangel, and with the trump of God: and the dead in Christ shall rise first. Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air; and so shall we ever be with the Lord.
Source: Catechetical Lectures (New Advent)