Matthew 12:31

Verses 31,32. In this place, and in Mr 3:28-30, Jesus states the awful nature of the sin of which they had been guilty. That sin was the sin against the Holy Ghost. It consisted in charging Jesus with being in league with the devil, or accusing him with working his miracles, not by the spirit or power of God, but by the aid of the prince of the devils. It was therefore a direct insult, abuse, or evil speaking, against the Holy Ghost--the Spirit by which Jesus worked his miracles. That this was what he intended by this sin, at that time, is clear from Mr 3:30, "Because they said he had an unclean spirit." All other sins--all speaking against the Saviour himself--might be remitted.