What is unforgivable sin of blaspheme against Holy Spirit?

What is the sin of blaspheme against the Holy Spirit? Can you accidentally blaspheme against the Holy Spirit? Will everyone who blasphemes the Holy Spirit go to hell?

I tell you the truth, all sin and blasphemy can be forgiven, but anyone who blasphemes the Holy Spirit will never be forgiven. This is a sin with eternal consequences.” He told them this because they were saying, “He’s possessed by an evil spirit.” (Mark 3:28-30 NLT)

“I can guarantee this truth: People will be forgiven for any sin or curse. But whoever curses the Holy Spirit will never be forgiven. He is guilty of an everlasting sin.” Jesus said this because the scribes had said that he had an evil spirit. (Mark 3:28-30 GWT)

“Assuredly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they may utter; but 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 3:28-30 NKJV)

“I assure you and most solemnly say to you, all sins will be forgiven the sons of men, and all the abusive and blasphemous things they say; but whoever [blasphemes against the Holy Spirit and His power [by attributing the miracles done by Me to Satan] never has forgiveness, but is guilty of an everlasting sin [a sin which is unforgivable in this present age as well as in the age to come]”— [Jesus said this] because the scribes and Pharisees were [attributing His miracles to Satan by] saying, “He has an unclean spirit.” (Mark 3:28-30 AMP)

What is blaspheme?

Comparing different translations is a very effective way of developing a deeper understanding of the passage. Sometimes it is helpful to look at the word pictures of the original Greek language…

blasphemes — 987 blasphēmēsē
to vilify; specially, to speak impiously — (speak) blaspheme(-er, -mously, -my), defame, rail on, revile, speak evil.
against — 1519 eis
to or into (indicating the point reached or entered), of place, time, or (figuratively) purpose (result, etc.); also in adverbial phrases
they were saying — 3004 elegon
(originally, “lay down to sleep,” used later of “laying an argument to rest,” i.e. bringing a message to closure; see Curtius, Thayer) – properly, to say (speak), moving to a conclusion (bringing it to closure, “laying it to rest”)
He has — 2192 echei
a primary verb; to hold
an unclean — 169 akatharton
impure (ceremonially, morally (lewd) or specially, (demonic) — foul, unclean

But he that shall blaspheme against the Holy Ghost,…. Against his person, and the works performed by him, by ascribing them to diabolical power and influence, as the Scribes did, hath never forgiveness: there is no pardon provided in the covenant of grace, nor obtained by the blood of Christ for such persons, or ever applied to them by the Spirit; but is in danger of eternal damnation. The Vulgate Latin reads it, and so it is read in an ancient copy of Beza’s, guilty of an eternal sin; a sin which can never be blotted out, and will never be forgiven, but will be punished with everlasting destruction; See Gill on Matthew 12:32.
Gill’s Exposition of the Entire Bible

Worshipping demons instead of God

These religious leaders were making a final conclusion that Jesus Christ (and the work he was doing by the Holy Spirit) were really, actually, demonic and satanic. This is much more than just using the name of the Lord in vain. The Greek word picture describes the closing argument by a professional prosecuting attorney in a criminal court case. It is done with full knowledge of the person, object, and idea being discussed. These religious leaders saw his miracles and heard him speak, yet they denied his deity and rejected his message. This cannot be done accidentally.

Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed [g331 anathema]: and that no man can say that Jesus is the Lord, but by the Holy Ghost. (1 Corinthians 12:3)

331 anathema
a man accursed, devoted to the direst woes (equivalent to doomed and so separated from Christ). cf. Matthew 16:16-17Matthew 22:43Mark 9:39John 13:13John 15:26; John 16:14-15Galatians 1:8; Galatians 3:13; 1 Corinthians 12:3; 1 Corinthians 16:22; 2 Corinthians 3:5; Romans 9:3Romans 10:91 John 4:2-3; .

Some deeply religious people are guilty

Don’t follow these religious leaders. Don’t reach the end of your life without believing that Jesus Christ is LORD and accepting His forgiveness from sins. Accept the grace offered by Jesus “to be forgiven for any sin or curse. (Mark 3:28)”

Not everyone who says to me, ‘Lord, Lord,’ will enter into the Kingdom of Heaven; but he who does the will of my Father who is in heaven. Many will tell me in that day, ‘Lord, Lord, didn’t we prophesy in your name, in your name cast out demons, and in your name do many mighty works?’ Then I will tell them, ‘I never knew you. Depart from me, you who work iniquity.’ (Matthew 7:21-23 WEB)

Then he will say also to those on the left hand, ‘Depart from me, you cursed, into the eternal fire which is prepared for the devil and his angels; (Matthew 25:41 WEB)