The Rapture is a favorite subject of mine because it is our great hope. I believe the Lord will take us to be spared from the Great Tribulation, so you know my personal bias. Regardless of the when (before, during or after the Tribulation) I believe there will be a Rapture.
The Apostle Paul describes the rapture in I Thessalonians 4:16-17. It is interesting that Paul only spent about three weeks with this church, and yet thought the doctrine of the Second Coming and the Rapture to be important enough to relate to the spiritually young Christians. Somehow, we are told that this a deep matter only to be discussed by mature Christians or those with lots of letters after their name.
The Lord Jesus alludes to the Rapture in the Olivet Discourse. In Matthew 24:40-41 He tells us that two people will be together doing normal daily activities, one will be taken and one "left behind." This indicates a special event and not a general resurrection or the judgement, because they had not died. And the word translated "taken" means "something joined to oneís self," or "to receive something transmitted." (Strongís Greek #3880) One will be "received" and the other will not. Jesus was describing what we call the Rapture.
The Old Testament tells of some being sequestered from the Lordís wrath (Isaiah 26:20 and Zephaniah 2:1-3). It speaks of a group mysteriously disappearing (Isaiah 57:1). The New Testament tells us that Christians will be protected from the coming wrath (I Thessalonians 1:10, 5:9, and the Revelation 3:10).
I may not know when it will occur, but there will be a Rapture because the Holy Scriptures tell us this. I may not know when the Rapture will occur but it appears the purpose of this wonderful event will be to protect us from the justifiable and righteous wrath of the Creator God Who made and owns this earth. May His name be praised forever.