What a frightening statement Jesus makes today! No forgiveness for eternity, if we blaspheme the Holy Spirit. Some people have taken this literally and feared that they have committed this unforgivable sin. They have come to believe that, no matter how sorry they are, God will not save them. This is not true. There is no sin which we cannot repent of. Indeed, the unforgivable sin is failing to repent.
What does it mean to blaspheme? It means to speak with contempt about holy things. Someone who has contempt for the Holy Spirit cannot be healed by the Holy Spirit. Jesus is offering freedom from evil spirits, but the scribes accuse him of offering this freedom under false pretence. What if one of those scribes was possessed by an evil spirit? Would he let Jesus free him by the power of the prince of demons? Probably not. So he would be forever bound.
It is like someone who has been poisoned and needs an immediate antidote. The one mistake which they must not make is to despise the antidote. If someone has diabetes and needs to start eating a healthy diet, the one mistake which they must not make is despising the advice of their doctor. They can call their doctor a mean old man, so long as they eat their vegetables.
When Jesus is talking about forgiveness, he is referring to the path of forgiveness. Anyone who starts down the path of forgiveness can be cured of all their sins, but if their sin is to refuse to make the journey of repentance, they necessarily remain forever in their sins. How could Jesus forgive the sin of despising forgiveness?
Which, then, merely leaves the question, why did Jesus call it “blaspheming the Holy Spirit” rather than “blaspheming forgiveness”? If he had said “blaspheming forgiveness”, we would understand right away, but because he said, “blaspheming the Holy Spirit” some people believe that because they once said something bad about the Holy Spirit they cannot be saved. Perhaps it was because the scribes would in principle believe in forgiveness, but they rejected the means of forgiveness.
If a person, in principle, believes that oxygen is necessary for life, but rejects breathing, they will die. It is necessary not only to accept forgiveness, but to accept forgiveness as it actually can be had. If a person believes in forgiveness but will not go to a priest and confess their sins and be forgiven by the power of the Holy Spirit, what good does that do them?