The Devil is that subtle...
1 Corinthians 15:56 "The sting of death is sin; and the strength of sin is the law."
The strength of this kind of false gospel is the law of dispensationalism, which declares that now is the "dispensation of grace".
The system of doctrine of dispensationalism goes deep into the core belief system of many churches in helping them establish confidence in their version of a God whose wrath has been pacified when Jesus Christ died at the cross. This event, according to them, is the beginning of the dispensation of grace, and this dispensation, according to their system of doctrine, will end at the onset of the rapture, right before the seven years of tribulation.
In another words, those who were saved during the dispensation of grace would never get to see the "man of sin" (2 Thessalonians 2:3) or suffer from the Great Tribulation because they would have been raptured to be with Christ when the “dispensation of Grace” should end at the onset of the next dispensation. Tribulation is only reserved for the Jews and the "tribulation saints" who were not saved during the dispensation of grace, they said.
The teachings of dispensationalism goes hand in gloves with the gospel of modern churches which teaches that the moment a sinner prays the sinner's prayer to accept Christ as Lord and Savior, God's wrath will be removed from him forever. That is the “grace of God” according to their gospel.
Christians in these kind of churches do not see themselves as potential candidates of the “falling away”, as in:
2 Thessalonians 2:3 "Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;"
On the contrary, they believe that Christ suffered once to save them from God's wrath for eternity. While this is true, the problem is that their doctrine of salvation is underpinned by another false doctrine, decisionism, which teaches that the moment a sinner demonstrates an outward act of repentance, such as praying a sinner's prayer, he is considered saved. The Devil is that subtle.