The Rapture
The Rapture, the blessed hope of believers, the calling home of the bride of Christ, is an event that will take even some professing Christians unaware. This event is imminent and many a believer are eagerly awaiting the catching up by our Lord to meet Him in the air, and see Him face to face for the first time, never to be parted from Him again.
The word Rapture does not appear in the bible, as it is an English representation of the Latin "rapio" which translates as "caught up". In Greek it is referred to as "harpazo", also translated as "caught up". The phrase "caught up" can be found in 1 Thessalonians 4:17, which states, "Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord." You can read it in context at Bible Gateway.
It is scripturally sound to make the statement that the Rapture will come before an event known as the 7-year tribulation. There is also evidence that once the Rapture occurs and puts and end to the age of grace, that coming to a saving knowledge of the Lord Jesus Christ will be nearly impossible for anyone who has heard the gospel message. The evidence of this is in 2 Thessalonians 2:7-12 which states, "For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: even him, whose coming is after the working of Satan with all power and signs and lying wonders, and with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. And for this cause God shall send them strong delusion, that they should believe a lie: that they all might be damned who believed not the truth, but had pleasure in unrighteousness."
In order to reject the truth, you have to have been introduced to the truth in the first place, at some point. Those who have been told the truth - that believing in the Lord Jesus Christ is the only way to be justified to God - but didn't believe it, are the ones who will receive the strong delusion after the rapture, when the age of grace comes to a close.
Believing in Jesus Christ doesn't mean believing He exists, it means believing only He can save you from eternal damnation (see Acts 4:12, John 14:6, or 1 Timothy 2:5). Once you truly believe in your heart that only He can save you, you are a new creation, and it changes the way you live your life. It changes your motivations, your thoughts, and your priorities, and guarantees your participation in the rapture, the blessed hope of believers. "Wherefore, comfort one another with these words." - 1 Thessalonians 4:18