Matthew Henry on 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.