The following is an excerpt from The MacArthur New Testament Commentary on Matthew 12 .

Therefore I say to you, any sin and blasphemy shall be forgiven men, but blasphemy against the Spirit shall not be forgiven. And whoever shall speak a word against the Son of Man, it shall be forgiven him; but whoever shall speak against the Holy Spirit, it shall not be forgiven him, either in this age, or in the age to come. (Matthew 12:31–32)

Few passages of Scripture have been more misinterpreted and misunderstood than these two verses. Because of their extreme seriousness and finality; it is critical to understand them correctly.

Jesus first stated that any sin and blasphemy shall be forgiven men. Although blasphemy is a form of sin, in this passage and context the two are treated separately-with blasphemy representing the most extreme form of sin. Sin here represents the full gamut of immoral and ungodly thoughts and actions, whereas blasphemy represents conscious denouncing and rejection of God. Blasphemy is defiant irreverence, the uniquely terrible sin of intentionally and openly speaking evil against holy God or defaming or mocking Him (cf. Mark. 2:7). The Old Testament penalty for such blasphemy was death by stoning (Lev. 24:16). In the last days blasphemy will be an outstanding characteristic of those who rebelliously and insolently oppose God (Rev. 13:5–6; 16:9; 17:3).

But even blasphemy, Jesus says, is forgiven, just as any other sin is forgiven when it is confessed and repented of. An unbeliever who blasphemes God can be forgiven. Paul confessed that, “even though [he] was formerly a blasphemer and a persecutor and a violent aggressor,” he was nevertheless “shown mercy, because [he] acted ignorantly in unbelief; and the grace of our Lord was more than abundant, with the faith and love which are found in Christ Jesus” (1 Tim. 1:13–14). “Christ Jesus came into the world,” the apostle continues, “to save sinners, among whom I am foremost of all” (v. 15). Peter blasphemed Christ with curses (Mark 14:71) and was forgiven and restored.

Even a believer can blaspheme, since any thought or word that sullies or defames the Lord’s name constitutes blasphemy. To question God’s goodness, wisdom, fairness, truthfulness, love, or faithfulness is a form of blasphemy. All of that is forgivable by grace. Speaking to believers, John said, “If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness” (1 John 1:9).

There is one exception, however: blasphemy against the Spirit shall not be forgiven. Even the person who blasphemes Jesus, who dares to speak a word against the Son of Man … shall be forgiven. Son of Man designates the Lord’s humanity, which He experienced in His time of humiliation and servitude during the incarnation. A person’s perception may not allow him to see more than the Lord’s humanity, and if he only misjudges at that level and speaks against Him in His humanness, such a word against the Son of Man can be forgiven. When a person rejects Christ with less than full exposure to the evidence of His deity, he may yet be forgiven of that sin if, after gaining fuller light, he then believes.

But the blasphemy against the Spirit was something more serious and irremediable. It not only reflected unbelief, but determined unbelief-the refusal, after having seen all the evidence necessary to complete understanding, even to consider believing in Christ. This was blasphemy against Jesus in His deity, against the Spirit of God who uniquely indwelt and empowered Him. It reflected determined rejection of Jesus as the Messiah against every evidence and argument. It reflected seeing the truth incarnate and then knowingly rejecting Him and condemning Him. It demonstrated an absolute and permanent refusal to believe, which resulted in loss of opportunity ever to be forgiven … either in this age, or in the age to come. Through this age (all of human history), such rejection is unforgivable. The age to come implies that through all of eternity there will be no forgiveness. In the age of human history and in the age of divine consummation, no forgiveness.

Scripture is clear that during His ministry on earth our Lord was submissive to the Father (John 4:34; 5:19–30) and empowered by the Spirit (Matt. 4:1; Mark 1:12; Luke 4:1, 18; John 3:34; Acts 1:2; Rom. 1:4). Peter said that God anointed Jesus of Nazareth “with the Holy Spirit and with power” (Acts 10:38).

Those who spoke against the Holy Spirit were those who saw His divine power working in and through Jesus but willfully refused to accept the implications of that revelation and, in some cases, attributed that power to Satan. Many people had heard Jesus teach and preach God’s truth, as no man had ever taught before (Matt. 7:28–29), yet they refused to believe Him. They had seen him heal every kind of disease, cast out every kind of demon, and forgive every kind of sin, yet they charged Him with deceit, falsehood, and demonism. In the face of every possible evidence of Jesus’ messiahship and deity, they said no. God could do nothing more for them, and they would therefore remain eternally unforgiven.