The idea of the rapture can be found in 1 Thessalonians 4:15-17. According to this, the Christians who have died before the rapture will rise from the dead and gather with Jesus in the clouds. Those that are alive during that time will follow those that have died to join with Christ in the clouds (vs. 17). Paul says that those who are alive during that time will be “caught up” with Jesus and the rest of the believers in the clouds before we are transported into heaven.
When Paul uses the word “caught up”, it’s the idea of catching something really fast…like you see a $20 bill on the floor and you quickly pick it up to keep it. That’s the idea. The rapture will happen so fast that no one will be able to see the believers being “snatched away” by Jesus Christ. It’s our belief that the Rapture will happen so quick that unbelievers will not be able to see what exactly happened.