Unforgivable sin

I believe accoding to the promises of the bible that we are forgiven all our sins; 1 John 1:9, "If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness." But there is an instance of a sin that Jesus has said to be unforgiven; Mark 3:29 - But whoever blasphemes against the Holy Spirit will never be forgiven; he is guilty of an eternal sin.

So what constitutes blasphemy against the Holy Spirit, the eternal sin that can never be forgiven?

Definition: Blasphemy is the act of showing contempt, insulting, or expressing a lack of reverence (respect) for God; the act of claiming the attributes of deity (God); defiant irreverence (disrespect / mockery) toward something considered sacred.

Some views that I have extracted;

The Life Application Study Bible commentary on Mark 3:28-29 has this to say, "Christians need not worry about this sin because this sin is attributing to the devil what is the work of the Holy Spirit. It reveals a heart-attitude of unbelief and unrepentance. Deliberate, ongoing rejection of the work of the Holy Spirit is blasphemy because it is rejection of God himself."

Thus, speaking against the Holy Spirit is equivalent to rejecting Christ with such finality that no future repentance is possible.

"If we refuse to accept the testimony given to us by the Holy Spirit, fight off His conviction of our sin, and never accept the truth, we will never come to Christ for salvation. In Christ, all our sins are forgiven. Therefore, no Christian can commit the unpardonable sin. Only an unregenerate person who refuses to come to Christ will die in his or her sins" [Freedom in Christ (Knoxville, Tennessee: FICM.org, 2002).].

"…once you accept Jesus, that part of the Holy Spirit's job is complete, thus you can't blaspheme His work. Naturally, He continues to work with you, and you can be stubborn and resist Him as a Christian, but you can't blaspheme Him. Live unproductively, carnal and unspiritual, possible. But commit the unpardonable sin? It's just not possible for a true Christian. Remember what Paul said: [Darrin Yeager (DYeager.org, 2002).] Rom 8:1 So those who are believers in Christ Jesus can no longer be condemned.

A true Christian cannot commit a sin for which there is no forgiveness. We are protected by the power of God (1 Peter 1:5). Although we can certainly grieve the Holy Spirit, he still seals us for the day of redemption (Ephesians 4:30). The Apostle Paul was confident "that He who has begun a good work in you will complete it until the day of Jesus Christ" (Philippians 1:6, NKJV).

Bear in mind, however, if someone who claims to be a Christian is responding to the Holy Spirit and Christ in a way very similar to that of the Pharisees, despite the strong witness of the Holy Spirit and abundant exposure to the truth of God's Word, it is highly doubtful that the person was ever saved. Only God knows for sure. The evidence clearly points to an unregenerate heart.
"…for a tree is known by its fruit. …For out of the abundance of the heart the mouth speaks" (Matthew 12:33-34, NKJV).

…If one's conscience is bothering him to the point that he feels he is too guilty for God to forgive, he has the assurance of God's Word that forgiveness is possible. The very fact that he is bothered by his sinfulness shows that the Holy Spirit has not abandoned him nor has God given him over to a depraved mind.