Because of this, God sends them a working of error, that they should believe a lie;
The way of salvation is clear enough in this verse and the preceding  2 Thessalonians 2:10.  Those who believe the truth and obey it shall be saved; those who do not believe the truth, but have pleasure in unrighteousness, shall be finally and irrevocably condemned.  For further discussion of the "man of sin," see excursus at the end of this chapter.