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. Several passages in the New Testament are frequently interpreted as referring to the unforgivable sin: Matthew 12:30-32: "Whoever is not with me is against me, and whoever does not gather with me scatters. Therefore I tell you, people will be forgiven for every sin and blasphemy, but blasphemy against the Spirit will not be forgiven. Whoever speaks 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 3:28–30: "Truly I tell you, people will be forgiven for their sins and whatever blasphemies they utter; but whoever blasphemes against the Holy Spirit can never have forgiveness, but is guilty of an eternal sin—for they had said, "He has an unclean spirit."" Luke 12:8–10: "And I tell you, everyone who acknowledges me before others, the Son of Man also will acknowledge before the angels of God; but whoever denies me before others will be denied before the angels of God. And everyone who speaks a word against the Son of Man will be forgiven; but whoever blasphemes against the Holy Spirit will not be forgiven." Hebrews 6:4–6: "For it is impossible to restore again to repentance those who have once been enlightened, and have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, since on their own they are crucifying again the Son of God and are holding him up to contempt.
Tobias Kippenberg, Victor Brasch, Michail Zervas, Michael Wolfgang Geiselmann, Martin Hubert Peter Pfeiffer, Arne Kordts, John David Jost