Question: "What is the blasphemy against the Holy Spirit?"
Answer: The case of "blasphemy against the Spirit" in the New Testament is mentioned in Mark 3:22-30 and in Matthew 12:22-32. The term blasphemy may be generally defined as "defiant irreverence." We would apply the term to such sins as cursing God, or willfully degrading things relating to God. It is also attributing some evil to God, or denying Him some good that we should attribute to Him. This case of blasphemy, however, is a specific one, called "THE blasphemy against the Holy Spirit" in Matthew 12:31. In Matthew 12:31-32, the Pharisees, having witnessed irrefutable proof that Jesus was working miracles in the power of the Holy Spirit, claimed instead that the Lord was possessed by the demon "Beelzebub" (Matthew 12:24). Now notice that in Mark 3:30 Jesus is very specific about what exactly they did to commit "the blasphemy against the Holy Spirit."
This blasphemy has to do with someone accusing Jesus Christ of being demon-possessed instead of Spirit-filled. There are other ways to blaspheme the Holy Spirit, but this was "THE" unpardonable blasphemy. As a result, the blasphemy against the Holy Spirit cannot be duplicated today. Jesus Christ is not on earth. but seated at the right Hand of God. No one can witness Jesus Christ performing a miracle and then attribute that power to Satan instead of the Spirit. Although there is no blasphemy of the Spirit today, we should always keep in mind there is an unpardonable state of existence--the state of continued unbelief. There is no pardon for a person who dies in unbelief. Continual rejection of the Holy Spiritís promptings to trust in Jesus Christ is the unpardonable blasphemy. Remember what is stated in John 3:16, "For God so loved the world that he gave his only begotten Son, that whosoever believeth in him should not perish but have eternal life." The only condition when someone would have no forgiveness is if that someone is not among the "whoever believes in Him."