Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
Great Apostasy
In Christianity, the term Great Apostasy is derived from the Second Epistle to the Thessalonians, in which the Apostle Paul informs the Christians of Thessalonica that a great apostasy must occur before the return of Christ, when "the Man of Sin is revealed, the Son of Destruction" (chapter ). As no such thing had yet occurred, Paul says that Christ cannot have returned yet.