28 Truly, I say to you, The sons of men will have forgiveness for all their sins and for all the evil words they say: 29 But whoever says evil things against the Holy Spirit will never have forgiveness, but the evil he has done will be with him for ever: 30 Because they said, He has an unclean spirit.
Matthew Henry's Commentary on Mark 3:28-30
Commentary on Mark 3:22-30
(Read Mark 3:22-30)
It was plain that the doctrine of Christ had a direct tendency to break the devil's power; and it was as plain, that casting of him out of the bodies of people, confirmed that doctrine; therefore Satan could not support such a design. Christ gave an awful warning against speaking such dangerous words. It is true the gospel promises, because Christ has purchased, forgiveness for the greatest sins and sinners; but by this sin, they would oppose the gifts of the Holy Ghost after Christ's ascension. Such is the enmity of the heart, that unconverted men pretend believers are doing Satan's work, when sinners are brought to repentance and newness of life.