“And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.”
And whoever speaks a word against the Son of Man will be forgiven, but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. The distinction between speaking against the Son of Man (forgivable) and speaking against the Holy Spirit (unforgivable in this age or the age to come) communicates the severity of the Pharisees' charge. Speaking against the Son of Man — failing to recognize Jesus, misunderstanding his identity — can be forgiven; deliberately attributing the Spirit's evident work to Satan is the sin that closes the door on forgiveness because it rejects the very means by which forgiveness comes.
Church Fathers on Matthew 12:32
The Lord had refuted the Pharisees by explaining His own actions, and He now proceeds to terrify them. For this is no small part of correction, to threaten punishment, as well as to set right false accusation.
He condemns by a most rigorous sentence this opinion of the Pharisees, and of such as thought with them, promising pardon for all sins, but releasing it to blasphemy against the Spirit; 'Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men.'
But it should be known that they are not forgiven to all men universally, but to such only as have performed due penitence for their guiltinesses. So by these words is overthrown the error of Novatian, who said that the faithful could not rise by penitence after a fall, nor merit pardon of their sins, especially they who in persecution denied.