http://www.khouse.org/articles/1995/35/
The Pre-Tribulation View
The Rapture is characterized in the New Testament as a "translation coming" (1 Corinthians 15:51- 52; 1 Thessalonians 4:15-17) in which the Lord comes for His church, taking her to His Father's House (John 14:3). However, at Christ's Second Coming with His saints, He descends from heaven to set up His Messianic Kingdom on earth (Zechariah 14:4-5; Matthew 24:27-31). The differences between the two events are harmonized naturally by the "pre-trib" position, while other views are not able to ac count comfortably for such differences.
A New Testament Mystery
Paul speaks of the Rapture as a "mystery" (1 Corinthians 15:51-54), that is, a truth not revealed until its disclosure by the apostles (Colossians 1:26). The Second Coming, on the other hand, was predicted in the Old Testament (Daniel 12:1-3; Zechariah 12:10; 14:4). In fact, the oldest prophecy uttered by a prophet was given before the flood of Noah and was of the Second Coming! It was given by Enoch, quoted in Jude 14-15.
The movement of the believer at the Rapture is from earth to heaven; at the Second Coming it is from heaven to earth. At the Rapture, the Lord comes for His saints (1 Thessalonians 4:16), while at the Second Coming the Lord comes with His saints (1 Thessalonians 3:13).
Post-tribulation Problems
One of the strengths of the pre-trib view is that it is better able to harmonize the many events of end-time prophecy because of the above distinctions. There are some awkward difficulties with the post-tribulational view:
1) The post-tribulation view requires that the church be present during the 70th week of Daniel (Daniel 9:24-27), even though it was absent from the first 69. This is in spite of the fact that Dan 9:24 indicates that all 70 weeks are for Israel. We believe the church must depart prior to the 70th week, before the final seven-year period (see our briefing package, Daniel's 70 Weeks, for further study).
2) The post-tribulation view denies the New Testament teaching of imminency--that Christ could come at any moment--since there are intervening events required in that view. We believe there are no signs that must precede the Rapture.
3) The post-tribulation view has difficulties with who will populate the Millennium
4 if the Rapture and the Second Coming occur at essentially the same time. Since all believers will be translated at the Rapture and all unbelievers are judged, because no unrighteous shall be allowed to enter Christ's Kingdom, then no one would be left in mortal bodies to start the population base for the Millennium.
4) Similarly, post-tribulationism is not able to explain the sheep and goats judgment after the Second Coming in Matthew 25:3- 46. Where would the believers in mortal bodies come from if they are raptured at the Second Coming? Who would be able to enter into Christ's Kingdom?
5) The Bride of Christ, the church, is made ready to accompany Christ to earth (Revelation 19:7-8, 14) before the Second Coming, but how could this reasonably happen if part of the church is still on the earth awaiting the Second Coming? If the Rapture of the church takes place at the Second Coming, then how does the Bride (the church) also come with Christ at His Return?