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 .
Indulgence
"When a person sins, he acquires certain liabilities: the liability of guilt and the liability of punishment." 
A mortal sin (one that is grave, or serious, in nature and is committed knowingly and freely) is equivalent to refusing friendship with God and communion with the only source of eternal life. The loss of eternal life with God, and the eternal death of hell that is the effect of this rejection, is called the "eternal punishment" of sin. The Sacrament of Penance removes the guilt and the liability of eternal punishment related to mortal sin. "Though your sins are like scarlet, they shall be white as snow; though they are red like crimson, they shall become like wool."