2 Thess: 3Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition; KJV

3Let no one deceive you in any way. For that day will not come, unless the rebellion comes first, and the man of lawlessness[b] is revealed, the son of destruction, ESV

perdition |pərˈdi sh ən| noun (in Christian theology) a state of eternal punishment and damnation into which a sinful and unpenitent person passes after death.

Son of perdition: Perdition means "destruction," the complete loss of well-being. It is really the opposite of salvation. To call him the son of perdition means his character is marked by this destruction. Moffatt says son of perdition essentially means the doomed one.

Unless the falling away comes first: The ancient Greek wording for falling away indicates a rebellion or a departure. Bible scholars debate if it refers to an apostasy among those who once followed God, or a general worldwide rebellion. In fact, Paul may have both in mind, because there is evidence of each in the end times (1 Timothy 4:1-3, 2 Timothy 3:1-5 and 4:3-4). But Paul's point is clear: "You are worried that we are in the Great Tribulation and that you missed the rapture. But you can know that we are not in the Great Tribulation, because we have not yet seen the falling away that comes first."

i. The falling away: The article makes it even more significant. This is not a falling away, but the falling away, the great and final rebellion.

ii. Some have suggested that the idea behind falling away is really a departure, in the sense of the rapture of the church. But a departure implies that the one leaving does so of his own accord and initiative, and this is not the case with the catching away of the church. In addition, the ancient Greek word in the New Testament (Acts 21:21), or in the Septuagint, always speaks of something sinful and negative.