I have occasionally seen folks mentioning that the sin against the Holy Spirit is attributing God's works to the devil. Um, no. That is called a mistake.
If you read the passage, it says:
The crowd came together again, so that they could not even eat. And when his family heard it, they went out to seize him, for people were saying, "He is beside himself." And the scribes who came down from Jerusalem said, "He is possessed by Beelzebul, and by the prince of demons he casts out the demons." And he called them to him, and said to them in parables, "How can Satan cast out Satan? If a kingdom is divided against itself, that kingdom cannot stand. And if a house is divided against itself, that house will not be able to stand. And if Satan has risen up against 'himself and is divided, he cannot stand, but is coming to an end. But no one can enter a strong man's house and plunder his goods, unless he first binds the strong man; then indeed he may plunder his house.
"Truly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they utter; but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin" — for they had said, "He has an unclean spirit."
What blaspheming the Holy Spirit refers to, in my humble opinion, is the persistence of the accusers. It's not simply the mistake of calling good evil and evil good. I believe that's forgivable. It's the persistence that's the issue here. Rather than admit they are wrong, they persist in accusing Jesus. Essentially, the problem is they keep arguing to the point where they accuse the Holy Spirit of being an evil spirit.
But this persistence, I believe, must be until the end of life. I don't think the problem is the Holy Spirit is touchy and if you say something bad about the Holy Spirit you are doomed. I think it means that if you just keep arguing until the end, you're in trouble. Jesus in the above passage doesn't accuse the scribes of committing the unforgivable sin, either. He's just saying that "all sins are forgiven" except this resistence to forgiveness and deliverance. The Scribes are on the edge of committing it.
So what is the sign you have blasphemed the Holy Spirit? I think an inability to repent. Not that you haven't repented -- I mean you can't. I don't mean regular human stubbornness, denial or self-justification throughout life -- I myself have seen that drop like a curtain in one second in the Holy Spirit's presence. Both in my case and others.
But I think that human stubbornness and self-justification can eventually yield into a place in your soul where you can't repent, because you don't want to.
My two cents.
