What is the falling away or apostasy of 2 Thess. 2:3?
Here’s what I think we can know for sure about this passage.
First, although the KJV translates it “a falling away,” the Greek text reads “the apostasia.” The presence of the definite article most likely suggests that Paul has in mind a definite event, probably one he had already told the Thessalonians about (2 Thess. 2:5).
Second, the word translated “falling away” by the KJV (apostasia) normally refers to a rebellion or an uprising against authority, whether political (1 Esdras 2:21; Josephus, Life 1.43) or spiritual (Josh. 22:22; Jer. 2:19; 2 Chr. 29:19). In the OT it always referred to spiritual rebellion and a turning away from God (cf. Ahaz in 2 Chron. 29:19). In the only other NT text where this word occurs (Acts 21:21), Paul was accused of teaching Jews to “revolt against or abandon” the law of Moses.
This understanding of apostasia suggests more than a lukewarm spirituality or a drifting into spiritual coldness. Rather, it points toward active rejection and rebellion against God. There is coming a time that will be “the rebellion” in which men turn against God.
These two pieces of information set 2 Thess. 2:3 apart from other NT texts that predict times of falling away from the faith (Matt. 24:10-12; 1 Tim. 4:1; 2 Tim. 3:1-9). Throughout history, the number of the faithful has waxed, generally during periods of persecution, and waned, generally during periods of relative prosperity.
Just a few decades after the Laodicean church had been founded, it was foundering with lukewarmness. Such “falling away” is a perennial problem. But 2 Thess. 2:3 addresses a specific period just preceding or concurrent with the revelation of the man of sin who will set himself up as God in a rebuilt temple in Jerusalem.