All the more reason to get to the bottom of what Jesus really means. He says that any sin and blasphemy shall be forgiven men except for blasphemy against the Holy Spirit. "Whoever shall speak a word against the Son of Man, it shall be forgiven him. But whoever shall speak against the Holy Spirit, it shall not be forgiven him, either in this age or in the age to come." So, even speaking against the Son of Man is a forgivable offense. Peter who denied Jesus three times was forgiven and restored. The mob who had called for Jesus' crucifixion, whom Peter preached to on the Day of Pentecost, were forgiven and baptized, three thousand souls. Even Saul the Pharisee who had persecuted Jesus by murdering his followers was forgiven and transformed into Paul the apostle.
So why isn't it okay to blaspheme against the Holy Spirit? First off, I don't think it's helpful to think of the distinction between blaspheming the Son of Man versus the Holy Spirit as a distinction of blaspheming the second person versus the third person of the Trinity. Because then you start wondering if the third person is somehow greater than the second person, and that's not the point.
Rather the distinction is about clarity of revelation. The true identity of the Son of Man is veiled to people's eyes, whereas the miraculous works of the Holy Spirit are an obvious sign of God's power. Those who fail to understand who the Son of Man is are spiritually blind, like those who stumble around in the darkness, who feel the objects they bump into but can't identify them. When Jesus asks, "Who do people say that I am?" he already knows there is confusion: some say he is Elijah, others say he is prophet, others say he is John the Baptist returned from the dead. Even when Peter confesses, "You are the Christ, the Son of the living God," moments later he falls into blindness again so that Jesus has to rebuke him with, "Get behind me, Satan!" The clear vision Peter had of the Son of Man's true identity instantly escapes him, and most never grasp it at all (Matthew 16:13-23).
The works of the Holy Spirit, on the other hand, are clear signs of divine power exploding into the realm of fallen humanity. A leper is cleansed, a blind man healed, a paralytic cured, a demon cast out. And yet the Pharisees say of such works, "This man casts out demons only by Beelzebul the ruler of the demons." They are calling the holy miracles of the Spirit demonic. They denounce the wondrous healings of the Spirit as evil. Mark helps to clarify what Jesus means when he speaks of blasphemy against the Holy Spirit in this parallel passage: [Jesus says,] "But whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin"--because they were saying, "He has an unclean spirit" (Mark 3:29-30). In this last editorial comment Mark makes clear that the eternal sin is condemning the unique manifestation of the Holy Spirit's power through the incarnate Christ as something unclean.
Take a look at this passage where Jesus acknowledges that even if you don't believe in him (i.e., the Son of Man), you should at least believe in the plain-as-day miracles he performs (i.e., the Holy Spirit):
The Jews took up stones again to stone him. Jesus answered them, "I showed you many good works from the Father; for which of them are you stoning me?" The Jews answered him, "For a good work we do not stone you, but for blasphemy; and because you, being a man, make yourself out to be God." Jesus answered them, ". . . If I do not do the works of my Father, do not believe me. But if I do them, though you do not believe me, believe the works, that you may know and understand that the Father is in me, and I in the Father" (John 10:31-33, 37-38).
Most people who saw the miracles of Jesus understood that the power of God was at work through him. They weren't quite sure who this man was--the return of Elijah? John the Baptist? Jeremiah?--but they knew he must be a holy man of some sort because of the works he performed. They were within the ballpark of knowing that there was some God-like thing going on. But the Pharisees not only refused to acknowledge the man but also his divine works, and they even called these miracles demonic and unclean. How far gone were they? The Spirit's works were meant to be obvious, undeniable revelation. They should have recognized the works of the Holy Spirit as the power of God just as they'd acknowledge the sky to be blue.
Few people in history had the privilege of seeing the miracles of Jesus by the power of the Holy Spirit. But for some, like the Pharisees, it only became an opportunity to reveal their wicked hard-heartedness by committing the greatest offense imaginable. They received a glimpse into heaven and they called it hell. Such a sin can't be forgiven because if you call what is undeniably holy Satanic, there is nothing left to redeem you. There is simply no hope for you.