Augustine of Hippo, on 1John 5:16

“He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that any man ask.”

“And this, perhaps, it is "to sin against the Holy Ghost:" i.e. through malice and envy to fight against brotherly charity after receiving the grace of the Holy Spirit: that sin which the Lord saith hath no forgiveness, either here or in the world to come. For the Lord in saying to the Pharisees, "Whosoever shall speak an evil word against the Son of Man," may have meant to warn them to come to the grace of God, and having received it, not to sin as they have now sinned. For now they have spoken an evil word against the Son of Man, and it may be forgiven them, if they be converted and believe and receive the Holy Spirit: which when they have received, if they will then have ill-will against the brotherhood and oppose the grace they have received, there is no forgiveness for them, either in this world or in the world to come.”

Imported from an open dataset — not yet checked against the printed edition.