Jesus said that blasphemy against the Holy Spirit cannot be forgiven.  Some think this blasphemy can happen in an instance by accident and some think this cannot happen today.  Let’s take a careful at what the Bible says.

The term blasphemy against the Holy Spirit is found only three times in the Bible, shown below.

Mat 12:31  “Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men.
Mat 12:32  Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come.

Mar 3:28  “Assuredly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they may utter;
Mar 3:29  but he who blasphemes against the Holy Spirit never has forgiveness, but is subject to eternal condemnation”—
Mar 3:30  because they said, “He has an unclean spirit.”

Luk 12:10  “And anyone who speaks a word against the Son of Man, it will be forgiven him; but to him who blasphemes against the Holy Spirit, it will not be forgiven.

All three of the passages clearly state that blasphemy against the Holy Spirit cannot be forgiven.  What led Jesus to make this statement?  Matthew and Mark give the context and reason.  We will look at Matthew.

Mat 12:22  Then one was brought to Him who was demon-possessed, blind and mute; and He healed him, so that the blind and mute man both spoke and saw.

Jesus miraculously healed this man, as he had many other people.

Mat 12:23  And all the multitudes were amazed and said, “Could this be the Son of David?”

The crowds loved it.

Mat 12:24  Now when the Pharisees heard it they said, “This fellow does not cast out demons except by Beelzebub, the ruler of the demons.”

The religious leaders accused Jesus of being demon possessed.  Matthew doesn’t mention this directly, but Mark does.

Mar 3:22  And the scribes who came down from Jerusalem said, “He has Beelzebub,” and, “By the ruler of the demons He casts out demons.”

They claimed it was by the power of the devil that He cast out demons.  The question is, did the religious leaders really believe their own accusation?  Or did they know Jesus was of God but were jealous of Him, the adoring crowds, and the miracles He performed?  The answer is, the Pharisees knew that Jesus was a teacher come from God.  John tells us this.

Joh 3:1  There was a man of the Pharisees named Nicodemus, a ruler of the Jews.
Joh 3:2  This man came to Jesus by night and said to Him, “Rabbi, we know that You are a teacher come from God; for no one can do these signs that You do unless God is with him.”

The Pharisees knew that Jesus was from God and cast out demons by God; yet they accused Him of being demon possessed.  And Jesus knew this because He knew their thoughts.

Mat 12:25  But Jesus knew their thoughts, …

Jesus proceeded to show the fallacy of their argument, perhaps for the benefit of crowd rather than the Pharisees.

Mat 12:25  But Jesus knew their thoughts, and said to them: “Every kingdom divided against itself is brought to desolation, and every city or house divided against itself will not stand.
Mat 12:26  If Satan casts out Satan, he is divided against himself. How then will his kingdom stand?
Mat 12:27  And if I cast out demons by Beelzebub, by whom do your sons cast them out? Therefore they shall be your judges.

Jesus then gets to the heart of the issue.  Jesus directs His response at their thoughts, not so much their words. 

Mat 12:31  “Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men.
Mat 12:32  Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come.

The Pharisees were knowingly and purposefully rejecting God.  Jesus’s statement about blasphemy against the Spirit, which will not be forgiven, was a warning to them that they were in danger of losing out on eternal life.

Blasphemy against the Spirit is not a slip of the tongue, or some hasty thoughtless comment.  It is not restricted to those who lived at the time of Jesus.  Blasphemy against the Spirit is knowingly and purposefully rejecting God to the point where it will not be forgiven. 

Why will this sin not be forgiven?  Is it because God refuses?  No.  God will forgive us if we confess our sins.

1Jn 1:9  If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.

If this sin will not be forgiven, even though God is willing to forgive, then the problem is with the sinner.  God is telling us that we can harden our hearts against God to the point of no return where we no longer want to repent and can never ever want to repent.  A man refusing to repent is like a man walking down a mountain side that’s getting steeper and steeper.  Eventually he slips and falls down the mountain, unable to save himself.  As another analogy, think of a stick being held upright.  It has flexibility to bend from the upright position, representing sin, and return, representing repentance.  But if the stick is bent too far it snaps in two, representing the impossibility of repentance.

Conclusion

Blasphemy against the Spirit is knowingly and purposefully rejecting God where the sinner hardens his heart to the point of no return where he can no longer repent and thus will not be forgiven.