The term ‘rapture’ is derived from the Latin word that is translated ‘being caught up’ in 1 Thessalonians 4:16-17:
“For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. 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, and so we will always be with the Lord.”
What will happen?
In 1 Thessalonians 4:13-5:11, Paul is concerned that the Thessalonian believers might misunderstand what happens to their fellow Christians who have died (1 Thessalonians 4:13). Paul explains that when Christ returns (i.e. at the end of this age, see Mark 13:24-27) He will descend from heaven. Those who have died in Christ will be raised first (1 Thessalonians 4:16). Then believers who are still alive at His coming will be caught up in the air. With those who have already been raised, we will meet the Lord together, and from that moment on, we will be with Him forever (1 Thessalonians 4:17). Therefore, the rapture signals the beginning of the New Heavens and the New Earth (Revelation 22:1). Essentially, the rapture refers to what will happen to believers at Christ’s return.
For Christians, then, Christ’s return is something we look forward to and long for. This hope is captured in the Bible’s closing prayer: “Come, Lord Jesus!” (Revelation 22:20). It also assures believers that they will be reunited with Christian friends and family who have already died. Therefore, Christians are not to grieve in the same way as those without hope (1 Thessalonians 4:13).
Be ready for Christ’s return
However, Christ’s return will not be joyful for all people. Revelation 6:12-17 describes what Christ’s return will be like for unbelievers:
“When he opened the sixth seal, I looked, and behold, there was a great earthquake. And the sun became black as sackcloth, the full moon became like blood. And the stars of the sky fell to the earth as the fig tree sheds its winter fruit when shaken by a gale. The sky vanished like a scroll that is being rolled up, and every mountain and island was removed from its place. Then the kings of the earth and the great ones and the generals and the rich and the powerful. And everyone, slave and free, hid themselves in the caves and among the rocks of the mountains, calling to the mountains and rocks, ‘Fall on us and hide us from the face of Him who is seated on the throne, and from the wrath of the Lamb, for the great day of their wrath has come, and who can stand?'”
Therefore, the rapture reminds us that we need to be ready for Christ’s return, which we can do by repenting and believing the gospel (Mark 1:15).
Note: Some Christians would separate the rapture (Christians being caught up with Christ) and the second coming (i.e. the final judgement and the start of the New Heavens and Earth). However, as J.I. Packer puts it, this view ‘has been widely held but lacks scriptural support’ (J. I. Packer, Concise Theology, 251.)).