Blasphemy against the Holy Spirit

Nature

In Christian hamartiology, eternal sin, the unforgivable sin, unpardonable sin, or ultimate sin is the sin which will not be forgiven by God. One eternal or unforgivable sin (blasphemy against the Holy Spirit), also known as the sin unto death, is specified in several passages of the Synoptic Gospels, including Mark 3:28–29, Matthew 12:31–32, and Luke 12:10, as well as other New Testament passages including Hebrews 6:4–6, Hebrews 10:26–31, and 1 John 5:16.

The unforgivable sin is interpreted by Christian theologians in various ways, although they generally agree that one who has committed the sin is no longer able to repent, and so one who is fearful that one has committed it has not done so.

Source: Wikipedia

Claim 
Matthew: "Whoever says a word against the Son of Man will be forgiven but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come." Mark: "All sins will be forgiven the sons of men, and whatever blasphemies they utter; but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin." Luke: "Every one who speaks a word against the Son of Man will be forgiven; but he who blasphemes against the Holy Spirit will not be forgiven." Why is blasphemy against the Holy Spirit unforgivable? How should this blasphemy be understood ? St. Thomas Aquinas replies that it is a question of a sin that is "unforgivable by its very nature, insofar as it excludes the elements through which the forgiveness of sin takes place."According to such an exegesis, "blasphemy" does not properly consist in offending against the Holy Spirit in words; it consists rather in the refusal to accept the salvation which God offers to man through the Holy Spirit, working through the power of the Cross. (Papal Encyclical, Dominum et Vivificantem, 18 May 1986).
Broader 
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Type 
(J) Problems under consideration