I used to believe in the pre-tribulation rapture, but it was actually the scripture which changed my mind.
The Church does teach the rapture, but calls it the Parousia , and it happens when Christ comes again.
Pre-Trib rapture thought believes that** the Rapture happens in Revelation 4:1** when the apostle is told “Come up here” – the rapture happens before all the “bad stuff” occurs to the world.
Their main reason for believing in a pre-tribulation rapture is various scripture such as Revelation 3:10 which says “I will keep you from the hour of trial that is coming on the whole world, to try those who dwell on the earth.” and I Thessalonians 5:9 which says “For God has not destined us for wrath, but to obtain salvation through our Lord Jesus Christ”. In other words, they say that those who have put their faith in Christ will be saved out of the world and will not come under the harsh judgements which are described in the book.
However, there is a huge clue in the scriptures which gives the timing of the rapture. I Corinthians 15:52 says that the rapture happens at the 7th Trumpet: "Listen, I tell you a mystery: We will not all sleep, but we will all be changed—in a flash, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, the dead will be raised imperishable, and we will be changed. This verse is one of the main verses which adherents of the rapture point to, to prove their position of a belief of a rapture.
So according to scripture, the rapture does not occur in Revelation 4:1, but at the last trumpet in Revelation chapter 11 which coincides with Christ’s 2nd coming: “Then the seventh angel sounded; and there were loud voices in heaven, saying, ‘The kingdom of the world has become the kingdom of our Lord and of His Christ; and He will reign forever and ever.’ And the twenty-four elders, who sit on their thrones before God, fell on their faces and worshiped God, saying, ‘We give You thanks, O Lord God, the Almighty, who are and who were, because You have taken Your great power and have begun to reign. And the nations were enraged, and Your wrath came, and the time came for the dead to be judged, and the time to reward Your bond-servants the prophets and the saints and those who fear Your name, the small and the great, and to destroy those who destroy the earth.’”
So this is something you might be able to point out to your friend, that according to the scriptures the rapture happens at the 7th Trumpet–not before the trumpets start blowing–as the adherents of the pre-trib rapture believe.