New Defender's Study Bible Notes
2:11 believe a lie. There is a definite article here—“the lie.” Those who have refused the truth will be given a strong delusion by God Himself when the man of sin is revealed. They will believe his lie, receive him as the god of this age, then perish with him.
2:12 damned. That is, “condemned after judgment.”
2:12 believed not the truth. Those who do not believe the truth of the glorious gospel of Christ when they have opportunity in this age, rejecting Him as Creator and Savior, are destined for damnation—that is, eternal punishment in the lake of fire. There will be no opportunity for them to be saved in the tribulation period, for their names will have been blotted out of the book of life (Revelation 3:5; 13:8).
However, there will indeed be a great multitude out of every tribe and nation saved during the tribulation period (Revelation 7:9,14). These will be men and women who never had a real opportunity to understand and receive the gospel before the rapture, but who will believe (often even suffering martyrdom for their faith) when they read or hear it during this coming time of judgment on earth.