That is a question Christian Theologians have been trying to answer for decades.
Here is one commentator's in depth study on it and one of the longest commentary I have seen on it, if thou art interested:
http://www.kingdombiblestudies.org/tablecontents.htm
http://www.kingdombiblestudies.org/savior/SOW1.htm#14
WHAT IS THE SIN?
What is the sin against the Holy Spirit? In the third chapter of Mark, we have the parallel passage to the text we just read in Matthew, the same record of these men coming around Jesus when they saw Him perform His mighty miracle for the poor man who could neither see nor speak. In order to keep the people from believing Jesus, they said the miracle was performed by the power of Satan. Notice the words of Jesus in verses 28-30: "Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith so ever they shall blaspheme. But he that shall blaspheme against the Holy Ghost has never forgiveness, but is in danger of eternal damnation: BECAUSE THEY SAID, HE HAS AN UNCLEAN SPIRIT." Ah - now there's a clue - the Pharisees' opposition to Jesus was not a spur of the moment, hotheaded fit of pique. These men knew what they were doing. Their schemes against Jesus were deliberate, calculated. A leading Pharisee, Nicodemus, once confided 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" (Jn. 3:2).......................
THERE IS NO UNPARDONABLE SIN!
*snip*
“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 speaks a word against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come" (Mat. 12:31-32).
I am glad that Jesus said that all manner of sin and blasphemy shall be forgiven men. I believe that is true. ALL manner. There is no kind of sin, which because of its kind, or manner, is unpardonable. The enemies of the truth of the ultimate salvation of all men have relied on this dissertation about the unpardonable sin given by our Lord, as their outstanding bulwark of defense against those who affirm that Christ is indeed the Saviour of all men, the Saviour of the world. Invariably, when the certainty of eternal torment is discussed and doubted, the sin against the Holy Ghost is brought forward as an impregnable defense against forgiveness hereafter for at least one sin. Few know how to reply. Here is what the Lord said: "But whosoever speaks against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come." On the surface it seems conclusive to the unthinking; and it has equally seemed so to learned theologians who have been trained in the channels of orthodox thinking. Yet, as a matter of fact, these words of our Lord are among the strongest collateral evidence that can be produced in support of the truth of the reconciliation of all men to God. Hearken! A sin against the Holy Spirit will never be forgiven in this "world," nor in the "world" to come.
While the King James version states that the sin against the Holy Spirit will not be forgiven in this world nor in the world to come, that is not quite the meaning of the Greek. The Greek word here translated "world" is AION. This word AION has been translated into fifteen different English words and phrases, many of which convey the wrong meaning entirely. The simple meaning of AION is "age." An AION is "an age." Two AION(S) are two "ages." A thousand AION(S) are a thousand "ages." Some of the passages where AION is found will give us added information concerning it. In Eph. 2:7 we find, "in the ages (aions) to come." In Col. 1:26 we find, "the mystery which has been hid from ages (aions)." In Eph. 2:2 we find, "you walked according to the course (aion) of this world." In Heb. 1:2 we find, "by whom also He made the worlds (aions)." In Hebrews 11:3 we find, "the worlds (aions) were formed by the word of God."
In about fifteen instances, such as Mat. 12:32, I Cor. 1:20, etc., we find it rendered "this world (aion)." Twice we find "this present world (aion)." In Gal. 1:4 we find, "deliver us from this present evil world (aion)." In Eph. 6:12 we find, "the rulers of the darkness of this world (aion)." In II Cor. 4:4 we find, "the god of this world (aion)." In I Cor. 2:6 we find, "the wisdom of this world (aion)." In Mk. 4:19 we find, "the cares of this world (aion)." How much clearer and understandable it would be if the translators had used the correct wordage instead of world! In Mk. 10:30 we find that there is not only this present aion, which is evil, but also "the world (aion) to come." Certainly this present age is an evil age, and the rulers of the darkness of this age are evil. Clearly God framed the ages, and there are not only "this age" and "the age to come," but there are also "the ages to come" (Eph. 2:7). Any thinking person should plainly see that if you translate a word which means an age by the word world, you immediately get the wrong idea. It is incorrect and brings nothing but confusion. There is a great deal of difference between the expression, "It shall not be forgiven him, neither in this world, neither in the world to come," and the expression, "It shall not be forgiven him in this age, nor in the age to come."
The translation in Mat. 12:32 of "world" instead of "age," has been the source of an altogether erroneous concept. This "world" and the "world to come" has become so indelibly impressed on the Christian mind as meaning "this life and eternity," that it is next to impossible quickly to reverse the trend of belief and direct it into sound thinking. It makes all the difference in the world when one understands that our Lord was not contrasting "this world" with that "great eternity out there somewhere," but merely pointing to two ages: this age and the age to come...............
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