Christianity and Judaism
In contrast to the Jewish view of being morally balanced, Original Sin refers to the idea that the sin of Adam and Eve's disobedience (sin "at the origin") has passed on a spiritual heritage, so to speak. Christians teach that human beings inherit a corrupted or damaged human nature in which the tendency to do bad is greater than it would have been otherwise, so much so that human nature would not be capable now of participating in the afterlife with God. This is not a matter of being "guilty" of anything; each person is only personally guilty of their own actual sins. However, this understanding of original sin is what lies behind the Christian emphasis on the need for spiritual salvation from a spiritual Saviour, who can forgive and set aside sin even though humans are not inherently pure and worthy of such salvation. Paul the Apostle in Romans and I Corinthians placed special emphasis on this doctrine, and stressed that belief in Jesus would allow Christians to overcome death and attain salvation in the hereafter.
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."