Forgiveness is the act of releasing someone from a debt or obligation. There are seven words in Scripture that denote the idea of forgiveness: three in Hebrew and four in Greek. No book of religion except Christianity teaches that God completely forgives sins. God remembers our sins no more (Heb. 10:17). God is the initiator of forgiveness (Col. 2:13).
There is only one sin for which the Father does not promise forgiveness: blasphemy against the Holy Spirit (Mark 3:28, Matt. 12:32). The contexts suggest this to be the sin of attributing to unclean spirits the work of the Holy Spirit.
For man to receive forgiveness, repentance is necessary (Luke 17:3-4). For the holy God to extend forgiveness, the shedding of blood is necessary (Heb. 9:22, Lev. 17:11). Forgiveness is based upon the sacrifice of Christ on the cross.