Answer: The concept of “blasphemy against the Spirit” is mentioned in Mark 3:22-30 andMatthew 12:22-32. The term blasphemy may be generally defined as “defiant irreverence.” The term can be applied 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 they did to commit “blasphemy against the Holy Spirit.”
This blasphemy has to do with someone accusing Jesus Christ of being demon-possessed instead of Spirit-filled. As a result, this particular incidence of blasphemy against the Holy Spirit cannot be duplicated today. Jesus Christ is not on earth—He is 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. The closest example today would be attributing the miracle of a redeemed person’s changed life to Satan’s power rather than to the effects of the indwelling Holy Spirit.
The blasphemy of the Spirit today, which is the same as the unpardonable sin, is the state of continued unbelief. There is no pardon for a person who dies in unbelief. Continual rejection of the Holy Spirit’s promptings to trust in Jesus Christ is the unpardonable blasphemy against Him. Remember what is stated in John 3:16: “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.” Further on in the same chapter is the verse “Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God's wrath remains on him” (John 3:36). The only condition wherein someone would have no forgiveness is if he is not among the “whoever believes in Him,” for it is he who “rejects the Son.”
Recommended Resource: Hard Sayings of the Bible by Kaiser, Davids, Bruce, & Brauch.