"For the Lord Himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air" (1 Thessalonians 4:16-17).
The event described by Paul in 1 Thessalonians is known to premillennialists as the rapture. It is viewed as occurring prior to the millennial reign of Christ. It, therefore, should not be confused with the resurrection of the unsaved, which occurs at the end of the millennium. Premillennialists differ as to the timing of the rapture, and generally hold to one of three positions (though there are others).
The pretribulation rapture position states that Christ will return for his Church prior to the 7-year tribulation period. Thus, believers will not experience the reign of antichrist.
The midtribulation rapture position states that Christ will return for his Church at the mid-point of the 7-year tribulation period. The second half of the tribulation is seen as the time when God's wrath is poured out upon a Christ-rejecting world. Since the Church is exempt from God's wrath, the Church will be raptured prior to this pouring out of God's wrath.
The postribulation rapture position states that the rapture will occur at Christ's second coming. The Church will be present on earth during the entire tribulation period, but will not experience God's wrath. It will, however, experience the antichrist's persecution.
All three positions are acceptable within orthodox Christianity. It is not an issue to break fellowship over.