Blasphemy of the Holy Spirit is attributing something done by the Holy Spirit to demons. That occurred when people claimed that Jesus’ miracles, done by the power of the Holy Spirit, were actions of demons.
Agreed...most people miss that part of the story. There is also the “sin unto death” but I don’t think that is the “unforgiveable sin”. Annanias and Saphira lied to the apostles and the holy Ghost about what they sold their property for and thus died but I don’t know that their souls were damned forever for it. Paul spoke of judging a sinning member...”releasing him to Satan for the destruction of his body so that his spirit could be saved in the day of resurrection.”
No Jesus seems to be saying that it is possible to so grieve the Spirit of God by those saying his acts of mercy were of the enemy, that persons may never be able to find forgiveness and peace with God. That is a horrible state to be in. I hope, when Jesus uttered this warning against blasphemy against the Holy Ghost,that many of the hearers took it to heart and that the Spirit regarded the episode as a lapse of judgment, a bit of brain flatulence for their sake. Jesus issued the warning of what would happen if they continued, he didn’t say they had all reached that place yet. “If you don’t believe in me, at least I would have you believe that the miracles were of God...any sort of blasphemy against the Son and the Father can be forgiven, but blasphemy against the Holy Spirit will not be forgiven” He said this because they accused him of performing miracles by the power of Satan. That was Jesus view of the “unforgiveable” sin.
Technically though some argue that to deny Jesus’ salvation and forgiveness and to die in an unsaved state is the “unforgiveable” sin but I think that is a technical error. Up to the point of death a man’s sins can be forgiven except for the Holy Ghost blasphemy, yet even that level can only be determined by the Spirit just how far a person went before the aggrieved Spirit sadly goes away. If some of the “near death” experience accounts of some Christians are to be believed, some were nearly dead and on the brink of hell when they cried out to Christ and he saved them right at the brink...their changed lives after recovery being a testimonial proof of having been saved “by the skin of their teeth”.
Certainly the Bible says a person may be woo’d by the spirit and for some, if they resist the Spirit, the Spirit will cease to strive with such a person at some point; in which case such a person may never know salvation,with their consciences seared to imperviousness to the effects of love and mercy.
But that is not the “blasphemy of the Holy Spirit which is the unforgiveable sin” that Jesus was talking about.