The below is something a sincere Christian student wrote, who is worried about the 'unpardonable sin':
"I would like to just know if what it says in Matthew is true. It states that every sin is forgivable, except if a person speaks badly about the Holy Spirit. I have attended a private Christian school and one day my Bible teacher was saying that a person is not forgiven if he/she speaks against the Holy Spirit. As he stated that… I thought something against the Holy Spirit. I did not mean to… it just happened. I prayed and asked forgiveness, but does that mean I am forgiven or eternally condemned? SINCERELY WORRIED"
It made me chuckle because I could relate.
There was a time in my pentecostal church life that I was worried about the unpardonable sin; but then later on, I figured out the unpardonable sin was nothing but speaking against Holy spirit and His gifts. I even thought all the baptists are doing 'unpardonable' sin as they speak against the gift of tongues, prophecy etc. I couldn't wait to see the baptists burning in the hell as the Pentecostals dancing in heaven. I even mentioned this 'revelation' to my pentecostal pastor and he agreed!
Yes, there is something called unpardonable sin; but the question is, what is it?
But whoever blasphemes against the Holy Spirit will never be forgiven; he is guilty of an eternal sin. - Mark 3:29
It's important to see the verse following this:
He said this because they were saying, "He has an evil spirit." In another words, they did not believe Jesus for who He is (God), and Jesus called it an unpardonable sin. Which in fact IS an unpardonable sin!
The same incident was recorded by Mathew as well:
Anyone who speaks a word against the Son of Man will be forgiven, but anyone who speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. - Mathew 12:32
Here, it is important to see what the purpose of sending the Holy Spirit was:
But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor will not come to you; but if I go, I will send him to you. When he comes, he will convict the world of guilt in regard to sin and righteousness and judgment: in regard to sin, because men do not believe in me; in regard to righteousness, because I am going to the Father, where you can see me no longer; and in regard to judgment, because the prince of this world now stands condemned. - John 16:7-11
The sin (singular) mentioned here is the sin of unbelief ('because men do not believe in me'). Holy Spirit convicts an unbeliever of their unbelief in Jesus and if they reject that conviction, it is a sin against Holy Spirit and it will not be forgiven in this age or in the age to come. The ONLY sin Holy Spirit ever going to convince people is the sin of unbelief.
As far as the believers are concerned, they have already repented of their unbelief and placed their faith in Christ Jesus and are free of any condemnation. Holy Spirit's job in a believer's life is to convince them of their righteousness in Christ ('He will guide you into all truth'). The truth of who we are in Christ.
There are no sin which is unpardonable other than the sin of unbelief, which has to be repented of. All other sins were judged on the body of Christ, has taken away from the eyes of God, never to see them again. Today, if somebody is condemning us due to our sins, it is either 'the accuser of the brethren' or one of his agents. Holy Spirit will never ever point us to our sins, instead He will always point us to Christ and His righteousness which is imputed to us.