Blaspheming the Holy Spirit – The Unpardonable Sin
During His physical life on earth, Jesus often exercised His Deity by performing miracles through the Divine power of the Holy Ghost. In Matthew 12:22-32, the Pharisees witness one of the Lord’s many miracles. Then, instead of believing on Jesus, they accused Him of performing miracles through the power of the Devil. He then told them that men could be forgiven for blasphemy (evil and hurtful speaking) against men and against Him, but that blasphemy against the Holy Ghost could NEVER be forgiven. A companion reference for this is found in Mark 3:30, where we are told WHY Jesus said this to them: “Because they said, he hath an unclean spirit.”
It is important to note that nothing is said about this particular sin after Calvary. It is only mentioned during the life of Christ on earth, while He was working genuine miracles by the power of the Holy Ghost. It is also needful to understand that blasphemy is a sin of the TONGUE. A person could not commit blasphemy with thoughts or actions. It was strictly a sin of the tongue, and it could only be committed by openly accusing Jesus Christ of working through Satanic power.
Some teach that this sin may still be committed today, but there is no scriptural support for this. In fact, when Jesus later speaks of the coming of the Holy Ghost to indwell believers, He said that the Holy Ghost would convict the world of three things: sin, righteousness, and judgment. He then said that the Holy Ghost would convict the world of SIN for ONE REASON: “because they believe not on me.” (John 16:7-11) It seems that if blasphemy against the Holy Ghost was to be the greatest sin of this age, that Jesus would have used this opportunity to warn us about it, but He warned us about UNBELIEF instead.
Some Charismatic groups, who profess to be LED by the Holy Ghost, are in the habit of accusing anyone who opposes them of blaspheming the Holy Ghost. For example, some Charismatics would say that I have blasphemed the Holy Ghost in this booklet, because I have written things in opposition to their practice of speaking in unknown tongues  and faith healing. That’s baloney. Even if they WERE doing all these things by the Holy Ghost (which they are not), it still would not be unpardonable to speak against it. Many people have spoken against great Christian works and then gotten saved later. The Apostle Paul is a good example (Acts 8-9). The blood of Jesus Christ cleanses us from ALL SIN (I John 1:9), and if you want to commit the unpardonable sin in this age, then you will have to reject Jesus Christ as your Saviour. Go ahead and reject Christ, and when you stand before God at the White Throne Judgment, you will NOT be forgiven.
Now we do realize that a person can reject Christ for so long that God the Holy Ghost pulls away and stops convicting that individual. In which case the individual never receives Christ, never receives forgiveness of sin, and goes to Hell (Pro. 1:23-33; Isa. 55:6-7; John 12:37-43), but only God knows when a person crosses that line. No man on this planet has any scriptural authority for telling someone that God will never forgive them for their sins. 
 For further study you may order PMI tract Speaking in Tongues by Dr. Mike.
 Copyright © 1998 James L. Melton- The Bible Believer’s Handbook of Heresies