What is the unforgivable sin?

Answer 1

This is a much debated question but I think the answer is clear. This question comes from the biblical statement of Jesus to the Pharisees. MAT 12:31 "Therefore I say to you, any sin and blasphemy shall be forgiven men, but blasphemy against the Spirit shall not be forgiven." So whatever the sin is, it is called blasphemy by God. The context of this verse explains to us what the unforgivable sin is.

Jesus has just healed a demon possessed man so that the man could see and talk. verse 22

The people were amazed but the religious rulers saw the same miracle and accused Jesus of working by the power of the devil. verse 24 Jesus makes is very plain that the devil would not work against himself because that would be self-defeating. v. 26 The only other alternative is that if Jesus did not work for the devil he would be working for God. This the Pharisees knew quite well. So, knowing this, the Pharisees deliberately attributed the work of Jesus to the devil. Jesus also said that he worked by the Spirit of God (which is the same thing as the Holy Spirit) So Jesus by the power of the Holy Spirit healed this man and the Pharisees said Jesus work by the power of the devil. In this context blasphemy is attributing the work of God to the devil.

Answer 2

Many will have different answers here but it seems to me that if someone is called to Christ by the Father (see John 6:44; 65). These 'called out' ones in their lifetimes will fully repent and be baptized to follow/imitate Jesus doing God's good works (see Ephesians 2:10). Now, after becoming part of the 'Firstfruits' of God, they 'blaspheme' or show defiant irreverence towards the ways and words of Christ, in effect reverting back to their old self before baptism, they commit the 'Unpardonable Sin' having been saved once and discounted it. Here is how Paul addresses it:

Hebrews 10:26-31New King James Version (NKJV)

The Just Live by Faith

26 For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. 28 Anyone who has rejected Moses' law dies without mercy on the testimony of two or three witnesses. 29 Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace? 30 For we know Him who said, "Vengeance is Mine, I will repay,"says the Lord. And again, "The Lord will judge His people."[c]31 It is a fearful thing to fall into the hands of the living God.