The Big Lie
The context of this passage is to comfort the Thessalonians who were under the
false impression that they were going through the tribulation period. Paul
writes to correct their theology and sets out a few guidelines of the tribulation
period. Within this explaination is a prophecy regarding a deception that would
come upon the whole world.
God desires that all be saved and come to the knowledge of the truth (1 Tim. 2:4-6).
But when people refuse to entertain the truth, He lets them pursue and experience
the consequences of falsehood (cf. Rom. 1:18-25). In fact God, as the Judge
of men, begins this judgment at the moment of their rebellion and subjects them
to the powerful delusion (energeian planes) which comes from choosing error
over truth. They choose to believe the lie and God sends them the delusion that is
inherent in their choice. This powerful judgment from God is justified by
the unbeliever's decision to refuse the truth. "The lie" is the claim that the
man of lawlessness is God.
(The Bible Knowledge Commentary, p. 720)