Reasons for the Pre-Trib Rapture:
Reason #1: Revelation 19:11-21 doesn't mention a resurrection. The Rapture is a resurrection of those "in Christ" (1 Thessalonians 4:13-18). Doesn’t it strike you as odd that Revelation 19:11-21, which is the clearest picture of the Second Coming of Christ, does not mention a resurrection? The Rapture will be the biggest event since the resurrection of Jesus where hundreds of millions of Christians will be resurrected and translated, yet there isn't any mention of it here. Don't you think it deserves at least one verse? The Rapture isn't mentioned because it doesn't occur at the second coming.
Reason #2: Zechariah 14:1-15 doesn't mention a resurrection. This is an Old Testament picture of Jesus returning to earth at the Second Coming. Again, no mention of a resurrection.
Reason #3: Two different pictures are painted. In the Old Testament, two different pictures are painted of the Messiah—one suffering (Isaiah 53:2-10, Psalms 22:6-8, Psalms 11-18) and one reigning as King (Psalms 2:6-12, Zechariah 14:9,16). As we look back on these Scriptures, we can see that they predicted two separate comings of the Messiah—the 1st coming as a suffering Messiah and the 2nd coming (still future) as a reigning King. In the New Testament, we have another picture added. Again, we have two pictures painted which don’t look the same. These two different descriptions of Jesus’ coming point to two separate events we call the Rapture and the Second Coming.
Reason #4: The Known Day and the Unknown Day Concerning the return of Jesus, the Bible presents a day we can't know and a day we can know. Matthew 25:13 says Jesus will return at an unknown time, while Revelation 12:6 says the Jews will have to wait 1,260 days for the Lord to return. The 1,260 days begins when the Antichrist stands in the Temple and declares himself to be God (Matthew 24:15-21, 2 Thessalonians 2:4). This event will take place at the mid-point of the seven year Tribulation (Daniel 9:27). The Antichrist has authority to rule for 42 months, which is 1,260 days (Revelation 13:4) and will be destroyed by Jesus at His Second Coming (Revelation 19:20, 2 Thessalonians 2:8). The known and unknown days happen at different times, meaning they are two separate events.
Reason #5: A door open in heaven (Revelation 4:1) The door in heaven is opened to let John into heaven. We believe John's call into heaven is prophetic of the Church being caught up at the Rapture (see Reason #6). In Revelation 19:11, heaven is opened again, this time to let the armies which are already in heaven out. This is the Church, which has been raptured at a previous time, following Jesus out of heaven at the Second Coming.
Reason #6: "Come up here." (Revelation 4:1) A voice called for the apostle John to "Come up here," and immediately he was in heaven. This seems to be a prophetic reference to the Rapture of the Church. The words "Come up here" are spoken to the two witnesses who are killed in the middle of the Tribulation, who are resurrected and ascend into heaven (Revelation 11:12). Therefore, the phrase "Come up here" could mean the church is raptured in Revelation 4:1. The word "church" is mentioned 22 times in Revelation 1-3, but is not mentioned again until Revelation 22:17.
Reason #7: The 24 elders have their crowns. After John is called up into heaven, he sees the 24 elders with their crowns (Revelation 4:4-10). We know that Christians will receive their rewards (crowns) at the Rapture (2 Timothy 4:8, 1 Peter 5:4). We will be repaid at the resurrection of the righteous (Luke 14:14). The elders could not have received their crowns unless the resurrection (Rapture) had taken place.
Reason #8: Holy ones are already with Jesus in heaven (Zechariah 14:5, Revelation 19:14). The armies in heaven, clothed in fine linen, follow Jesus out of heaven at His Second Coming (Revelation 19:14, Zechariah 14:5, Colossians 3:4). These are not angels because Revelation 19:8 tells us the fine linen is the righteousness of the saints. In order to come out of heaven we first have to go in, indicating a previous Rapture.
Reason #9: Kept from the hour of testing (Revelation 3:10) Revelation 3:10 says we will be kept out of the hour of testing which will come upon the whole earth (the Tribulation). Some wrongly believe that "keep" means to keep through, or protect through the Tribulation. Suppose you approach a high voltage area with a sign that says, "Keep Out." Does that mean you can enter and be protected? No, it means you are forbidden from entering the area. But this verse also says He will keep us from the hour of testing. It is not just the testing, but the time period. If a student is excused from a test, he still may have to sit in the class while others take the test. But if he is excused from the hour of testing, he can go home. The Church will be called home before the hour of testing.
Reason #10: Angels don't resurrect people when they gather them for judgment. When the angels are sent forth to gather the elect at the Second Coming (Matthew 24:29-31), some have wrongly interpreted this as the Rapture. There is a huge problem with this interpretation. If we are resurrected at this time, why would we need angels to gather us? In the resurrection, we will be like the angels (Matthew 22:30) and able to travel in the air at will. Obviously, these people who are gathered are not resurrected, therefore it can't be the Rapture. No one would claim the wicked are raptured at this time, yet Matthew 13:39-41, and Matthew 13:49 says the angels will not only gather the elect, but also the wicked. This gathering is not a resurrection.
Reason #11: Both wicked and righteous both can't be taken first. 1 Thessalonians 4:13-17 says the righteous are taken and the wicked are left behind. Matthew 13:30, and Matthew 13:49 says the wicked are taken first and the righteous are left behind. These verses point to two separate events, the Rapture and the Second Coming.
Reason #12: Jesus returns from the wedding. When Jesus returns to earth at the Second Coming, He will return from a wedding (Luke 12:36). At the Rapture, Jesus is married to His bride, the Church (Matthew 25:10). After the wedding, He will return to earth.
Reason #13: Jesus will receive us to Himself, and not us to receive Him (John 14:2-3). Jesus said He would prepare a place for the Church in heaven, and then He would come again to receive us to Himself. Why would Jesus prepare a place for us in heaven and then not take us there? At the Rapture, He will come to receive us to Himself, "that where I am (heaven), there you may be also." If the Rapture occurred at the same time as the Second Coming, we would go up to the clouds and then immediately come back to earth. That would contradict John 14:2-3.
Reason #14: The one who restrains is taken out of the way. In 2 Thessalonians 2:6-7, Paul says "the one who restrains will be taken out of the way" before the Antichrist can be revealed. We believe this refers to the Rapture because the Church is clearly the biggest obstacle to the Antichrist becoming a world ruler.
Reason #15: Paul says comfort one another with these words in reference to the Rapture or catching up mentioned in 1 Thessalonians 4:16-18. Now, what comfort is there in hearing these words from Paul about being caught up into the air if we have to go through the Tribulation period? It makes no sense.
Source Used:
http://makinglifecount.net/
(Important Note: It appears I do not agree with this site's version of Soteriology, but I do agree with the majority of their article on their defending the Pre-Trib Rapture).