What is the falling away?
Source: Homily by St. Chrysostom
2 Thessalonians 2:10-12 "For because they received not the love of the truth, that they might be saved; for this cause God will send them a working of error, that they should believe a lie: that they all might be judged who believed not the truth, but had pleasure in unrighteousness."
"That they might be judged." He does not say, that they might be punished; for even before this they were about to be punished; but "that they might be condemned," that is, at the dreadful Seat of Judgment, in order that they might be without excuse. "Who believed not the truth, but had pleasure in unrighteousness." He calls Christ, "the Love of the Truth." "For because," says he, "they received not the love of the truth," For He was both, and came for the sake of both, both as loving men, and on behalf of things that were true.
"But had pleasure," he says, "in unrighteous ness." For he came to the destruction of men and to injure them. For what will he not then work? He will change and confound all things, both by his commandments, and by the fear of him. He will be terrible in every way, from his power, from his cruelty, from his unlawful commandments. BUT FEAR NOT. "IN THOSE THAT PERISH" HE WILL HAVE HIS STRENGTH.