My understanding is blasphemy against the Holy Spirit is the lack of repentance.
My understanding in Catholicism is it’s the disbelief that God can and/or won’t forgive one’s sins in the sacrament of reconciliation
There is no pardon for a person who dies in his rejection of Christ. The Holy Spirit is at work in the world, convicting the unsaved of sin, righteousness, and judgment (John 16:8). If a person resists that conviction and remains unrepentant, then he is choosing hell over heaven. “Without faith it is impossible to please God” (Hebrews 11:6), and the object of faith is Jesus (Acts 16:31). There is no forgiveness for someone who dies without faith in Christ.
God has provided for our salvation in His Son (John 3:16). Forgiveness is found exclusively in Jesus (John 14:6). To reject the only Savior is to be left with no means of salvation; to reject the only pardon is, obviously, unpardonable.
So if the unrepentant sinner remains in that hardened condition till death, he or she has committed the unpardonable sin since they have rejected the only pardon there is.
There are a few parts of repentance:
Remorse with the heart, asking forgiveness with the tongue, work with the limbs and resolve not to repeat (the offense).
The last one is the most telling of the blasphemy. If a person asks forgiveness, and then repeats the act, they are not sincere in their prayer and are most times using God for an excuse to continue the sin. Probably the most disrespectful to using God as a crutch are homosexuals that declare themselves Christians asking forgiveness then repeating the act as it is shunned in most Bibles as the laying of same sex people as being with the other sex.
An example:
There are two verses from Leviticus that figure in the debates over the Bible and homosexuality. First of all Leviticus 18:22, which says:
You shall not lie with a male as with a woman; it is an abomination.
And the second one is similar. It comes from Leviticus 20:13:
If a man lies with a male as with a woman, both of them have committed an abomination; they shall be put to death; their blood is upon them.
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