Paul soothed the fears of the Thessalonians: the Day of the Lord, which begins with darkness and moves to light, had not yet begun. The Lord Jesus would come for His bride before pouring out His wrath on the unbelieving world (1 Thess 1:10, 4:13 - 5:11). Neither the coming of the Lord Jesus Christ and our gathering together unto Him had happened. And before the Day of the Lord occurs, there will be two great events: the falling away and the revelation of the man of sin.

I. Deception (2 Thess 2:3, 5). Satan’s greatest weapon is deception (exapatao). It was the weapon he used against Eve (2 Cor 11:3). Satan is a created being like everything else in the universe (Gen 1:1; Col 1:16). He is knowledgeable, knowing even the Bible (Mt 4:1-9), but is not all-knowing. He is powerful (Heb 2:14-15; 1 Jn 5:19), but not all-powerful. He is in the world (Mt 4:11), but not all-present. Even today, he has the ability to appear as an angel of light, but because of his limitations, he uses others to minister on his behalf (2 Cor 11:14-15; Rev 12:9).
The Biblical word deception means to fully lead astray by a trick. The Thessalonians had been shaken by what or who they thought was reliable (1 Thess 2:2), but they were not to fall for the tricks. He’d already taught them the truth about the Day of the Lord, now they needed to hold to it.
Paul taught eschatology, even to new believers. It wasn’t a secondary issue. It concerns the Person and nature of Jesus. It is also practical because it’s a motive to godly living (1 Jn 3:2-3; 4:17-81; 2 Pet 3:11, 14).

II. Error (2 Thess 2:3). The early church of Bible days was no different from the church today except for one thing: the early church was newly created. It was far from being pure, perfect, or powerful; it was made up of people. Every epistle of the New Testament reveals the early church was riddled with doctrinal errors, and doctrinal errors always produce errors in practice (Gal 1:6-9; 2 Pet 2:1-22; Jude). It was not something we should attempt to re-create or restore
Early doctrinal errors included that the resurrection of the dead had already occurred (18" class="scriptRef">2 Tim 2:18); circumcision of the flesh was necessary to be saved (Gal 5:2-11); Jewish laws, ceremonies, and festivals were necessary to follow (Col 2:16); worship of angels (Col 2:15, 18); Jesus was a spirit not human (1 Jn 4:2-3); Jesus was an exalted angel (Heb 1:1-14).

III. Apostasy (2 Thess 2:3). The falling away (apostasia) describes an aggressive revolt or rebellion; a deliberate defection from or abandonment of a previously held belief. Apostasy is a deliberate falling away from the truth of God’s Word; an apostate is someone who once professed salvation but whose heart was never regenerated.
Apostates are not saved people who lose their salvation. God promises not to lose anything belonging to Him (Jn 10:28, 29; Phil 1:6; 1 Pet 1:5). Instead, like Judas Iscariot, they were never saved at all (1 Jn 2:19). One of the proofs of genuine faith in Jesus is how persecution and trials are met; Paul gave thanks because the Thessalonians passed this test of their faith (Mt 13:20-21; 2 Thess 1:3-5).
There have always been apostasies, both in the Old Testament history of Israel, and in the New Testament record of the church (1 Tim 4:1-3; 2 Tim 3:1-5, 13; 4:3-4; Heb 3:12). What Paul writes to the Thessalonians about, however, is different. This is the apostasy, one in particular, greater than any other in both scope and depth, deceiving the elect if it were possible (Mt 24:24). It will be worldwide and by God’s will (2 Thess 2:9-12). It is what Jesus spoke of His second coming not finding the faith on the earth (Lk 18:8). When Jesus returns, the faith will not be present on earth.