Nicodemus once said to Jesus: "Rabbi, we know that You are a teacher come from God; for no one can do these signs that You do unless God is with him." (John 3:1,2)
Nicodemus was a Pharisee and "a ruler of the Jews", that is to say he was a member of the Sanhedrin, the judicial high court which included scribes, Pharisees, and the chief priests.
The scribes and Pharisees, and other members of the Sanhedrin, had obviously discussed the identity of Jesus amongst themselves. The conclusion they had come to was that Jesus had, indeed, "come from God".
"We know," said Nicodemus.
In the parable of the wicked vinedressers (Matt 21:33-45; Mark 12:1-12; Luke 20:9-19), the landowner (God) plants a vineyard (Israel) and leaves it in the care of vinedressers. In time, the landowner (God) sends servants (the prophets) to the vineyard but the vinedressers beat them, stone them, and murder them.
"Then last of all he sent his son to them, saying, 'They will respect my son.' But when the vinedressers saw the son, they said among themselves, 'This is the heir. Come, let us kill him and seize his inheritance'. So they took him and cast him out of the vineyard and killed him." (Matt 21:37-39)
Notice, if you will, that the vinedressers recognise the son for who he is and consciously, wilfully and defiantly choose to kill him.
In telling the parable, Jesus reveals that the "vinedressers" knew exactly who He was and knew they were going to kill the Son of God.
And notice at the end of the parable, what Matthew, Mark, and Luke all add - namely:
"Now when the chief priests and Pharisees heard His parables, they knew that He was speaking of them." (Matt 21:45) "They knew He had spoken the parable against them." (Mark 12:12) "And the chief priests and the scribes ... knew He had spoken this parable against them." (Luke 20:19)
In other words, it was as if Jesus said to them: "I know that you scribes, Pharisees, and chief priests know that I am the Son of God, and that you are going to kill me."
On one occasion Jesus performed a spectacular miracle by healing a man who was demon-possessed, blind and dumb.
And all the multitudes were amazed and said, "Could this be the Son of David?" Now when the Pharisees heard it they said, "This fellow does not cast out demons except by Beelzebub, the ruler of the demons." (Matt 12:23-24)
Knowing their thoughts (12:25), Jesus said: "Every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come." (Matt 12:31-32) Mark's account of the same incident adds: "'he who blasphemes against the Holy Spirit never has forgiveness, but is subject to eternal condemnation' - because they said, 'He has an unclean spirit'." (Mark 3:29-30)
For this reason, Jesus could say to the scribes and Pharisees: "Serpents, brood of vipers! How can you escape the condemnation of Gehenna?" (Matt 23:33)
Face to face with Jesus Christ, knowing exactly who He was, not just that He had "come from God", but that He was the Son of God - the scribes and Pharisees were able to look on incarnate goodness and call it incarnate evil. They consciously, wilfully and defiantly attributed to Satan that which was plainly and manifestly the miraculous operation of the Holy Spirit.
To consciously, wilfully and defiantly reject the work of the Holy Spirit - is the unforgivable sin.
The preaching of the gospel, or good news, of the forgiveness of sins is the work of the Holy Spirit (1 Peter 1:12)
Therefore, those who consciously, wilfully and defiantly reject the gospel, fully aware that that is what they are doing, are consciously, wilfully and defiantly rejecting the work of the Holy Spirit. That is the unforgivable sin.
Why is it unforgivable?
Not because Jesus refuses to forgive, but because the person consciously, wilfully and defiantly refuses to repent and accept the forgiveness freely being offered.
It is as if the person says: “I am fully convinced that you are Jesus, the Son of God; I am completely aware of how much you love me; I absolutely understand that all my sins can be forgiven. But I don’t want your love; I don’t want your forgiveness; I utterly and totally reject and scorn you; I spit in your face”.
