ISB ~ Matthew 12 v31

blasphemy against the Spirit:i.e., the sin of attributing to Satan the work of God. It is a mature spiritual hardness that directs sinners away from God’s mercy and ends in final impenitence. One who blasphemes the Spirit cannot receive forgiveness when he refuses to repent and seek forgiveness. It is this sin that the Pharisees commit in 12:24 (CCC 1864). See note on Mk 3:29.