Matthew 12:31 - The Unpardonable Sin

Wherefore I say unto you, All manner of sin and blasphemy shall
be forgiven unto men: but the blasphemy against the Holy Ghost
shall not be forgiven unto men. Mat 12:31 (KJV)

The particular function of the Spirit is to bring conviction and
repentance, and make men receptive to the invitation of Christ. Hence hearts
that hate God and blaspheme Christ (I Tim 1:13) may yet be convicted
and brought to repentance by the Spirit. But he who rejects every
overture of the Spirit removes himself from the only force that can lead
him to forgiveness (Jn 3:36)... The OT describes these as sinning
"with a high hand" (Num 15:30, ASV); for them no atonement was
possible. [Wycliffe Bible Commentary]

Anxiety about having committed this sin is a sure sign that one
has not committed it. The words warn against presumption and do not
limit God's grace. If you are convicted by the Holy Spirit to ask for
forgiveness, you may be sure God will forgive. [Disciple SB]

There is no sin that God has not overcome through Christ. That
means that no one ever has to fear going beyond the scope of God's
grace or power. Sometimes people despair because they have committed
certain sins that to them seem unforgivable. But no matter what their
failure has been, God can and will forgive their sin if they come to Him
in repentance (Acts 2:38; 1 John 1:9).
At the same time, it is possible to willfully place oneself
beyond the grace of God - to persist in rebellion and sin and resist
His call to repentance....
Is there an "unpardonable sin?" Not for those who cry out like
the tax collector in a parable of Jesus, "God, be merciful to me a
sinner!" (Luke 18:13). But those who, like the Pharisee in the same
parable (as well the Pharisees in this incident), trust to their own
self-righteousness, reject Christ, and slander His Holy Spirit - they reveal a
spiritual cancer so advanced that they are beyond any hope of healing and
forgiveness. [Word In Life SB]

The unpardonable sin is the... deliberate and irreversible
hardness of heart. Sometimes believers worry that they have accidently
committed this unforgivable sin. But only those who have turned their
backs on God and rejected all faith have any need to worry. Jesus said
they can't be forgiven-not because their sin is worse than any other,
but because they will never ask for forgiveness. Whoever rejects the
prompting of the Holy Spirit removes himself or herself from the only
force that can lead him or her to repentance and restoration to God.
[Life Application SB]

Blasphemy against the Holy Spirit, or the unpardonable sin,
consists of progressive resistance to truth that culminates in a final
and irrevocable decision against it, deliberately made in the full
knowledge that by so doing one is choosing to pursue his own course of
action in opposition to the divine will. The conscience is seared by
continued resistance to the impressions of the Holy Spirit, and one may
hardly be aware that he has made the fateful decision. [SDA
Commentary]

A person whose conscience troubles him may solve the problem and
remove the tension in one of two ways: He may yield to the transforming
power of the Holy Spirit, and respond to the promptings of the Holy
Spirit by making wrongs right with God and man, or he may sear his
conscience and eliminate its painful promptings by silencing the Holy
Spirit (see Eph. 4:30). The person who takes the latter course cannot
repent, because his conscience has been forever made insensitive, and he
does not want to repent. He has deliberately placed his soul beyond
the reach of divine grace. His persistent perversion of the power of
choice results in the loss of the power to discern between good and
evil. Evil finally appears to be good, and good appears to be evil.
[SDA Commentary]

They do despite to the Spirit of grace, until its voice is no
longer heard, and they are left to the delusions which they have
chosen. PP635

Christ told them plainly that in attributing the work of the
Holy Spirit to Satan, they were cutting themselves off from the
fountain of blessing. Those who had spoken against Jesus Himself, not
discerning His divine character, might receive forgiveness; for through the
Holy Spirit they might be brought to see their error and repent.
Whatever the sin, if the soul repents and believes, the guilt is washed
away in the blood of Christ; but he who rejects the work of the Holy
Spirit is placing himself where repentance and faith cannot come to
him. It is by the Spirit that God works upon the heart; when men
willfully reject the Spirit, and declare It to be from Satan, they cut off
the channel by which God can communicate with them. When the Spirit
is finally rejected, there is no more that God can do for the soul.
DA321,2

There is in man a Spirit-given faculty which enables him to
recognize goodness and truth when he sees them...
A man can lose any faculty if he refuses to use it. This is true
in any sphere of life. It is true physically; if a man ceases to
use certain muscles, they will atrophy. It is true mentally; many a
man at school or in his youth has acquired some slight knowledge of,
for example, French or Latin or music; but that knowledge is long
since gone because he did not exercise it. It is true of all kinds of
perception. A man may lose all appreciation of good music, if he listens to
nothing but cheap music; he may lose the ability to read a great book,
if he reads nothing but ephemeral productions; he may lose the
faculty of enjoying clean and healthy pleasure, if he for long enough
finds his pleasure in things which are degraded and soiled.
Therefore a man can lose the ability to recognize goodness and
truth when he sees them. If he for long enough shuts his eyes and ears
to God's way, if he for long enough turns his back upon the
messages which God is sending him, if he for long enough prefers his own
ideas to the ideas which God is seeking to put into his mind, in the
end he comes to a stage when he cannot recognize God's truth and
God's beauty and God's goodness when he sees them. He comes to a stage
when his own evil seems to him good, and when God's good seems to him
evil.
That is the stage to which these Scribes and Pharisees had come.
They had so long been blind and deaf to the guidance of God's hand
and the promptings of God's Spirit, they had insisted on their own
way so long, that they had come to a stage when they could not
recognize God's truth and goodness when they saw them. They were able to
look on incarnate goodness and call it incarnate evil; they were able
to look on the Son of God and call him the ally of the devil. The
sin against the Holy Spirit is the sin of so often and so
consistently refusing God's will that in the end it cannot be recognized when
it comes even full-displayed.
Why should that sin be unforgivable? What differentiates it so
terribly from all other sins? The answer is simple. When a man reaches
that stage, repentance is impossible. If a man cannot recognize the
good when he sees it, he cannot desire it.  If a man does not
recognize evil as evil, he cannot be sorry for it, and wish to depart from
it. And if he cannot, in spite of failures, love the good and hate
the evil, then he cannot repent; and if he cannot repent, he cannot
be forgiven, for repentance is the only condition of forgiveness.
It would save much heartbreak if people would realize that the one
man who cannot have committed the sin against the Holy Spirit is the
man who fears he has, for the sin against the Holy Spirit can be
truly described as the loss of all sense of sin....
It is a law of life that we will hear only what we are listening
for and only what we have fitted ourselves to hear.
There is a story of a country man who was in the office of a
city friend, with the roar of the traffic coming through the windows.
Suddenly he said, "Listen!" "What is it?" asked the city man. "A
grasshopper," said the country man. Years of listening to the country sounds
had attuned his ears to the country sounds, sounds that a city man's
ear could not hear at all. On the other hand, let a silver coin
drop, and the chink of the silver would have immediately reached the
ears of the money-maker, while the country man might never have heard
it at all. Only the expert, the man who has made himself able to
hear it, will pick out the note of each individual bird in the chorus
of the birds....
It is the law of life that we hear what we have trained
ourselves to hear; day by day we must listen to God, so that day by day
God's voice may become, not fainter and fainter until we cannot hear
it at all, but clearer and clearer until it becomes the one sound
to which above an our ears are attuned. [Barclay Commentary]

Our Lord warns that the human heart can be so pounded and beaten
down with the traffic of sin that it becomes completely insensitive
to the gospel.  This is the heart that knows no repentance, no
sorrow over sin, no guilt, and no concern for the things of God.  It
allows itself to be trampled by an endless procession of evil thoughts,
cherished sins, and ungodly activities.  It is careless, callous,
indifferent, never broken up or softened by conviction or sorrow for
wrongdoing  This is the heart of the fool described in Proverbs.  The fool
hates knowledge, and resists instruction.  The fool despises wisdom
and says in his heart there is no God.  He will not hear.  His mind
is closed.  And he does not want to be bothered with a gospel
invitation.
Many people have hearts like that.  You can shower them with
seed, but it just lies there.  It does not penetrate.  And it does not
stay very long before Satan comes and takes it away completely.  Each
time you try to witness to such a person, you must start again at the
beginning.
Dry, hard, soil on the edge of the field does not necessarily
signify someone who is anti-religious.  Some of the hardest individuals
in the world remain on the fringes of true religion.  But because
sin has hardened their hearts they are utterly unproductive and
unresponsive to God.  [John F. MacArthur, Jr.; Time With God SB re
Mat.13:1-17]

God Gave Pharaoh Into Hands of Self. Every additional evidence
of the power of God that the Egyptian monarch resisted, carried him
on to a stronger and more persistent defiance of God. Thus the work
went on, finite man warring against the expressed will of an infinite
God. This case is a clear illustration of the sin against the Holy
Ghost. "Whatsoever a man soweth, that shall he also reap." Gradually
the Lord withdrew His Spirit. Removing His restraining power, He
gave the king into the hands of the worst of all tyrants,--self (RH
July 27, 1897). 1BC1100

The greatest danger in putting off the decision to live for
Christ is not so much the soon return of Christ or even the end of
probation which precedes it, but the hardening of the heart that results
from such a decision and that soon makes one unable to make the
decision to live for Christ.  [Pastor Arthur Gibbs]