The "catching up" or rapture of the church will happen before the beginning of the seven years of the Great Tribulation. "Because you have kept My command to persevere, I also will keep you from the hour of trial which shall come upon the whole world, to test those who dwell on the earth. Behold, I am coming quickly! Hold fast what you have, that no one may take your crown" (Revelation 3:10-11). The rapture is a great event that will happen very quickly—as in the "twinkling of an eye." "Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; nor does corruption inherit incorruption. Behold, I tell you a mystery: We shall not all sleep, but we shall all be changed—in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality" (1 Corinthians 15:50-53). When the church disappears, all the people in the world, especially those who know a little about the scriptures, will be terrified and cry bitterly, without any consolation.
On the other hand, the rapture will be the most marvelous event for those who love the Lord and walk in Him. l Thessalonians 4:13-17 describes that great event, where the church will be caught up in the air to be always with the Lord. Jesus will not come down to the earth, as in His second coming after the Great Tribulation (Zechariah 14:4), but we now look for his "glorious appearing" (Titus 2:13) when he catches us up to be with Him. There are some who believe the church will go through the Great Tribulation, but how could it be our "blessed hope" to wait for that time of trials? How could we "comfort one another with these words" (1 Thessalonians 4:18, 5:11), waiting for the Great Tribulation? "For God did not appoint us to wrath, but to obtain salvation through our Lord Jesus Christ" (1 Thessalonians 5:9).
Jesus will come for His church, "that He might present her to Himself a glorious church, not having spot or wrinkle or any such thing, but that she should be holy and without blemish" (Ephesians 5:27). This is the church of the rapture, and He will have nothing less than this! It is a church with born-again members who know God and walk in the Spirit. They are known by their fruits, and because they love one another as Christ loves them.