Luke 12:10
10 And whosoever shall speak a word against the Son of man, it shall be forgiven him: but unto him that blasphemeth against the Holy Ghost it shall not be forgiven.
The Grace New Testament Commentary - Luke 12:10
12:10 In this context Jesus instructs His disciples about two kinds of negative responses to Him. First, "anyone who speaks a word against the Son of Man," probably pertains to those who initially respond negatively to Him on the mere basis of His humanity. This saying does not promise a blanket forgiveness for all irrespective of belief. Rather, it delimits those for whom forgiveness still exists as a possibility.
Second, others recognized the Spirit-empowered miracles that testify of Jesus' identity as the Messiah and yet harden their hearts against Him (e.g., John 9:24-31). "Him who blasphemes against the Holy Spirit" represents those unbelievers who intuitively understood God's handiwork or "fingerprints" in the ministry of Jesus and the early church and yet verbally denied Him.
Charles Bing - Grace, Salvation, and Discipleship - The Unforgivable Sin, Matthew 12:31-32 (cf. Mark 3:28-30)
(Salvation) Interpretation: A person can commit this sin that makes salvation impossible, or if he is saved, will cause him to lose his salvation.
Second (Salvation) Interpretation: A person can commit this sin that shows his heart is hardened to the Holy Spirit's convicting work that brings a person to salvation.
It is unfortunate that both unbelievers and believers have lived under the fear of committing this sin and thinking they have been disqualified from salvation. That this is A Truth is clear from whom Jesus is addressing. The audience are the unbelieving Pharisees and scribes who accuse Jesus of an allegiance with Satan (Matt. 12:24-30; Mark 3:22-27). Their verbal accusation prompts Jesus' reply about the sin that cannot be forgiven. Eternal salvation is at issue because this sin can never be forgiven and brings eternal condemnation (Matt. 12:32; Mark 3:29).
Jesus is not speaking of Israel's national rejection of Him, because He says "anyone," which denotes individuals. Also, the warning is about a sin more specific than unbelief in Jesus as Savior. Neither does it seem to be the specific sin of accusing Christ of satanic allegiance, as terrible as that is. Jesus says that blasphemies can be forgiven (Matt. 12:31; Mark 3:28). There is only one blasphemy that cannot be forgiven, and it is not specifically blasphemy against Christ, but against the Holy Spirit. Some interpret this as a sin that can only be committed by unbelievers when Christ is present performing miracles either in His lifetime or in the future kingdom. The issue, however, seems to be the heart attitude more than the time period.
What makes the most sense of this difficult saying is that Jesus speaks of a willful and slanderous rejection of the Holy Spirit's testimony about Christ. This sin is revealed in the perverse verbal accusation that Jesus Christ is in league with the devil. The Father witnesses to the Son both through prophecy and His verbal approval at Christ's baptism. The Son witnesses through His own words and works. These witnesses are external. But the Holy Spirit witnesses through His internal convicting ministry (John 16:7-11). When the Spirit convinces an unbeliever about who Jesus Christ is, and that person nevertheless accuses Him of being satanic, he has committed blasphemy against the Holy Spirit. Matthew's discussion that follows this warning emphasizes how one's words reveal one's heart condition so that "by your words you will be condemned" (Matt. 12:33-37). The accusation that Jesus is of the devil reveals the moral blindness of a person who would call light darkness. It displays a heart hardened beyond hope of forgiveness, because there is nothing left to appeal to the conscience when the Holy Spirit's testimony is rejected and slandered. Any unbeliever who blasphemes the Holy Spirit demonstrates a spiritual condition that precludes a receptive attitude toward the gospel.
According to this interpretation, someone who knowingly and maliciously rejects and slanders the Holy Spirit's convicting ministry about the person of Christ could commit this sin today. It would be hard to know when someone knowingly rejects the Holy Spirit's testimony and is not doing it out of ignorance, but God knows.
If there is a (Discipleship message) present in this warning, it is by implication. If you are a believer, then you have responded positively to the Holy Spirit's testimony about Christ. This should bring assurance that you cannot commit this sin and your salvation is not in jeopardy. If a believer worries about committing this sin, it is a testimony that he is still responding positively to the Holy Spirit's witness. Also, as believers, we have the assurance that God's grace covers every sin (Rom. 5:20; Col. 2:13). As for an unbeliever, if he worries about committing this sin, it is also a testimony that he is prone to respond positively to the Holy Spirit's testimony about Christ. We can say this emphatically: Those who believe in Jesus Christ as Savior are saved and have all their sins forgiven.