Let no one deceive you in any way. For it will not be, unless the departure comes first, and the man of sin is revealed, the son of destruction,
The portion of the Christian church in Paul’s view would be the non-genuine Christians who compose Christendom. "Christendom" refers to all professing Christians, genuine and non-genuine. Such a departure had begun in Paul’s day (1 Timothy 4:1-3; 2 Timothy 4:3-4; James 5:1-8; 2 Peter 2; 2 Peter 3:3-6; Jude). However it had not yet reached the proportions predicted to characterize "the apostasy" about which Paul had instructed his readers when he was with them (cf. 2 Thessalonians 2:5). When the Rapture takes place and all true Christians leave the earth, this apostasy will overwhelm the human race.