“Truly, I say to you, all sins will be forgiven the children of man, and whatever blasphemies they utter, but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin.” Mark 3:28-29
Clearly, as quoted in Mark 3:29, Jesus is singling out the unique attitude one is to have toward the third person of the Holy Trinity, the Holy Spirit: …whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin. Jesus paid for all sin by His holy precious blood, so how can any sin be unforgiveable? To answer this question one must discern the unique work of the Holy Spirit, a work not directly ascribed to the Father or the Son.
That unique work of the Holy Spirit is the miracle of connecting sinful human beings to the salvation earned by the cross and empty tomb of Jesus. This conversion miracle is described as “being born of the Spirit,” or “believing in Jesus.” As recorded in John 3, Jesus explains this miracle of being born of the Spirit: Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit [5,6]. Later in John 3 Jesus explains the results of believing or not believing in Him: Whoever believes in him [Jesus] is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God [18]. Here we see the horrible consequence of not being connected to Christ’s salvation—of not believing in Jesus. Jesus explained that such an unbeliever is condemned already. Why does such a person stand condemned? If someone does not believe in Christ’s salvific work, they remain in their sins; there is no forgiveness: unless you believe that I am he you will die in your sins [Jn 8:24].
In his Small Catechism, Luther described the foundational work of the Holy Spirit this way: “I believe that I cannot by my own reason or strength believe in Jesus Christ my Lord or come to Him; but the Holy Spirit has called me by the Gospel…” If it is essential for one’s forgiveness and eternal salvation that one believe in Jesus as Lord and Savior, and if we are totally incapable of doing this, then one begins to realize why the sin against the Holy Spirit is unforgiveable. To blaspheme the Holy Spirit is to reject and profane His person and work. This can and does happen as one rejects the Gospel by which the Holy Spirit comes to sinful man. When one persistently rejects the Gospel and thus the Spirit’s powerful work of conversion, such a person remains apart from Christ Jesus, and thus apart from His cleansing blood, and thus apart from eternal life.
So how does one know whether he/she has committed this most horrendous sin? First of all, a person who has committed the unforgiveable sin does not care one way or the other. If you are concerned about whether you have committed the unforgiveable sin, then you have not committed it. Second, do not rely on your own efforts or zeal in relation to Jesus, but realize the tremendous value of Holy Baptism. Jesus, as quoted above in John 3, describes this wondrous sacrament as the foundational means by which we are regenerated and thus justified in Christ Jesus. He describes it as being born of water and the Spirit. Are you baptized? Then you have received the gift of the Holy Spirit, you have been born again NOT by any effort you have set forth, but by the Holy Spirit, and whether you “feel” this or not, it is an objective reality. And unless you have rejected the Gospel given to you in Holy Baptism, you remain a forgiven child of God. You have not committed the unforgiveable sin.