According to Jesus, there is only one unforgivable sin, the blasphemy against the Holy Spirit. All sins and blasphemies will be forgiven them, except the blasphemy of the Holy Spirit. It wont be forgiven, in this life or the next. If this is the case, it is really important to know what this sin is and what it isn’t. So it can be avoided and correctly assessed.
In reality only the Lord can know for sure whether a person has truly blasphemed the Holy Spirit or not. For He alone knows the hearts of all. It isn’t a sin that can be done in ignorance, but its something that’s committed with full knowledge and awareness. Calvin’s description of this sin is as follows:
“He sins against the Holy Spirit, who while so constrained by the power of divine truth that he cannot plead ignorance, yet deliberately resists, and that merely for the sake of resisting.”
I would agree with this definition. In light of this, this is why we as believers must leave the final judgment with God, because there are people who would appear to be blaspheming the Holy Spirit but are doing it in ignorance and not with a full knowledge or awareness. For example, it would appear the Apostle Paul before his conversion had committed this sin, just like some of the other Pharisees. Yet Paul says he blasphemed in ignorance and from unbelief, and for this reason he obtained mercy.
“Even though I was once a blasphemer and a persecutor and a violent man, I was shown mercy because I acted in ignorance and unbelief.” 1 Timothy 1:13 NIV.
To the naked eye, it would have appeared Paul had blasphemed the Spirit, just as the others, but its a good thing God can correctly assess the whole heart. He saw that Paul did it out of ignorance, and not against a full knowledge and enlightenment in a deliberate sense. In short its a relief to trust God with this and the final judgment to come!