Eternal sin
In Christian hamartiology, eternal sins, unforgivable sins, or unpardonable sins are sins which will not be forgiven by God. One eternal or unforgivable sin (blasphemy against the Holy Spirit) is specified in several passages of the Synoptic Gospels, including , , and .
Nikolay Guryanov
Once he was asked what he considered to be the most dangerous sin in the souls of people? Father Nikolai answered: "Unbelief! This is frightening." - Even with Christians? - "Yes, even, with Orthodox Christians".