There are many sins. All are forgivable but one. Even the sin of rejecting Christ is forgivable if the rejection is out of a heart of doubt or unbelief, and if the unbeliever later repents and believes in Jesus Christ as his/her Lord and Savior. Every adult is doubtful and unbelieving ... before they repent and believe. But, it is different, and unforgivable, when it is "Blasphemy against the Holy Spirit", of which Jesus spoke in these two verses....
"Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men. And whosoever speaketh a word against the Son of man, (Jesus) it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come." Matt.12:31-32.
Why does Jesus say that speaking against Him (Jesus, "the Son of man"), and other blasphemies will be forgiven ... "but the blasphemy against the Holy Ghost shall not be forgiven"? A person may not be aware of exactly who Jesus is, whether the Bible is true or not, whether God is true or not, and speak against all of it, but later, believe, repent and be forgiven and saved, as was Paul. The same is not true of the blasphemy of the Holy Spirit. Here is why. The Holy Spirit's place in the Trinity is to "prove" to human hearts their guilt of sin, their need for righteousness and the certainty of judgement. When the Holy Spirit has "proven" and convinced the lost soul of his need for Christ, forgiveness and redemption, and that soul knows God is real and Jesus came to save him, but he still rejects, with rebellion, what the Holy Spirit has convinced him of .... that is Blasphemy of the Holy Spirit. The Holy Spirit proved God's case, but the guilty sinner not only rejected what he now knew to be true, but took sides against it.
This is what Jesus was alluding to when He said, "And when he (the Holy Spirit) is come, he will reprove the world of sin, and of righteousness, and of judgment .... Of righteousness, because I go to my Father, and ye see me no more." John 16:8 & 10. Whereas no man has ever seen the face of God (Jn.1:18) because God does not personally appear to men, and Jesus came to bring the message of God and the Gospel of salvation, it is the Holy Spirit who "reproves" or proves the truths of God to the hearts of men. What God ordained, Jesus delivered, but it is the Holy Spirit who convicts, convinces, and "proves" to the very souls of humanity that it is all true. So when the Holy Spirit has thoroughly proved and convinced a person that God is real, and they are sinners ripe for judgement, in need of righteousness, and that Jesus died for their sins and will save them, and they know that they know that it is true ... but reject the witness of the Holy Spirit anyway and take sides against Him, that is unforgivable. That is the Blasphemy of the Holy Spirit, and that is the sin of Lucifer.
Saul of Tarsus blasphemed Christians and Christ Himself, and persecuted them,
("Saul, breathing out threatenings and slaughter against the disciples of the Lord...." Acts 9:1) but he did not blaspheme the Holy Spirit. He was fanatically religious but sincerely believed he was "doing God a service" Jn.16:2. He did not believe Jesus was the Christ (Messiah) of the Jews until Jesus struck him down with light on the Road to Damascus. That light not only blinded Saul, but opened his spiritual eyes and he said, "Lord who art thou" and Jesus sent him to a Christian, Ananias, to hear the Gospel, be saved and baptized. Saul's name was changed to Paul, when he was saved, and he later testified ..."(I) was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief. 1 Tim.1:13. If he had not done it "ignorantly", but knowingly, he would not have obtained God's mercy but would have been guilty of blasphemy of the Holy Spirit. This verse signifies the difference between the sin of rejection done "ignorantly in unbelief" and the sin of rejection done "rebelliously with certain knowledge" that you are wrong and Christ right. Unrepented of rejection done "Ignorantly in unbelief" is forgivable if repented of in acceptance of Christ by grace through faith. Not so with the blasphemy of the Holy Spirit when a person already knows the truth of Christ with certainty and still rejects the witness of the Holy Spirit that Jesus is the prophesied Messiah, Son of God, and Savior. You see, believing in Jesus is of no benefit if the believing sinner rejects Christ as his Savior anyway, and refuses to repent and surrender his will and life to the LORD. "Therefore to him that knoweth to do good, and doeth it not, to him it is sin." James 1:17.
Even the Devil "believes in Jesus", but does not submit in sincere repentance and acceptance of Him as his LORD and cannot now do so. It is too late for him. Satan has always known exactly who Jesus was and is, but it didn't save him because he knew the truth about God and Christ before Genesis one, when he was Lucifer, in heaven with God, Christ and the Holy Spirit. But Lucifer rejected the God he knew was God and fought against Him. (Isa.14:12-15). That is Unforgivable and the reason Lucifer can never be saved. He already has known the truth of God and hated it and fought against what he knew to be the truth of God. "Thou believest that there is one God; thou doest well: the devils also believe, and tremble." James 2:19. You believe there is one God? Good for you ... but the devils believe that much.
Then there was the case of Legion, the Demoniac, demon possessed, lost, miserable, controlled by Satan who himself, recognized and knew who Jesus was. But Legion, when he heard Jesus, did not commit the Blasphemy of the Holy Spirit. Instead, he accepted Christ, was saved and delivered from Satan. But the devils who already knew exactly who Jesus was, and hated Him anyway, were cast out of Legion into the swine. Mark 5:1-17.
There are few sins so bad as religious heresy and corruption. All of the High Council, Religious Court (Sanhedrin) of the Jews, had strong knowledge of their coming Messiah, and knew Jesus fit the description perfectly, but just one of them resisted the others and came to ask Jesus sincere questions, under cover of darkness.... and was converted. "There was a man of the Pharisees, named Nicodemus, a ruler of the Jews: The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him." John 3:1-2. Note Nicodemus said, "we know" referring to the Jewish High Council of which he was a member. That body of Old Testament scholars "knew" who Jesus was, and rejected Him in spite of His fulfillment of all of the Messianic prophecies. It was the Holy Spirit, through the O.T. scriptural prophecies that convinced them Jesus was their Messiah ... But their rejection turned into strong rebellion and they conspired to kill Jesus.... anyway. That mixture of certain knowledge, rejection and rebellion is blasphemy of the Holy Spirit
who convinced them through their own Bible prophecies.
Here is one of the most astounding, unimaginable portions of scripture in the Bible. We see the entire council of these Pharisees, having heard Jesus's message, seen His miracles, and recognized Him as their Messiah ... But now realizing they might lose their position, income, prestige and followers, began plotting a way of doing away with Him. Their High Priest, Caiaphas, steps up before them and says to them, "Do you know who we are dealing with? Don't you realize how this will affect us if we acknowledge who this man is? Our Bible prophets of old foretold his coming in great detail ... He is the Messiah and 'it is expedient for us that he die for the people, and that the whole nation perish not'" And then it says that Caiaphas, the High Priest listed the prophecies of Jesus, "not of himself", but from the scriptures "that Jesus should die for the nation of Israel" and not just for them "but also he would gather together in one the children of God." That certain knowledge is what launched their vicious attack upon their known Messiah, and led to His crucifixion. "Then from that day forth they took counsel together to put him to death." That is
Blasphemy of the Holy Spirit.
Here is where it happened in John 11...
"Then gathered the chief priests and the Pharisees a council, and said, What do we? for this man doeth many miracles. If we let him thus alone, all men will believe on him: and the Romans shall come and take away both our place and nation. And one of them, named Caiaphas, being the high priest that same year, said unto them, Ye know nothing at all, Nor consider that it is expedient for us, that one man should die for the people, and that the whole nation perish not. And this spake he not of himself: but being high priest that year, he prophesied that Jesus should die for that nation. And not for that nation only, but that also he should gather together in one the children of God that were scattered abroad. Then from that day forth they took counsel together for to put him to death." John 11:47-53.
They took the killing of Jesus upon themselves, to fulfill the prophecies, and
schemed to have their Roman masters do the vile deed. That, my friend, is The Blaspheme of the Holy Spirit who had "proven" and convinced them that Jesus was the Jewish Christ, Messiah of prophecy, but they rejected Him and sought ways to kill Him anyway.... since it was prophesied.
The blasphemy of the Holy Spirit reveals itself in the impenetrable callousness of the hopelessly lost soul ... "Who being past feeling have given themselves over unto lasciviousness, to work all uncleanness with greediness." Eph. 4:19. "Speaking lies in hypocrisy; having their conscience seared with a hot iron." 1 Tim.4:2. "Past feeling" with no conscience" is the definition of the self-centered, sociopathic narcissist of whom we see many in politics and positions of power in today's world.
If you still have a desire to be right with God ... saved from your sins, you have not committed this sin and there is still hope for you. .. But come to Him now.
"...Sirs, what must I do to be saved? And they said, Believe on (not just "in") the Lord Jesus Christ, and thou shalt be saved, and thy house." Acts 16:30-31.