It seems to me the issue of sin and the forgiveness of sin has a lot to do with how the people of God have viewed their relationship with God over time. Tracing the history of Israel as viewed by the various traditions and editors of the Pentateuch, and the historical books, God seems in the mind of the people to demand blood sacrifice for many categories of sin. God also seems to demand the first born human, but will accept an unblemished first born sheep or ox in substitution.

The progression of the scriptures (is this a maturing thought?) seems to reveal a God who is more forgiving and who extends more grace.

The pinnacle of God's grace seems to rest then on the sacrificial Christ event, where God assumed human form and became God's own sacrifice. One that did away with the notion of God's demand for blood and opened the pathways of human awareness for the possibility of an unfettered, intimate relationship based only on God's grace and desire for human/divine relationship and not on any sacrifice, acts, or deeds of our own. Thus, in essence, the sacrificial death and resurrection did away with the old sacrificial system so that faith and not sacrifice becomes the basis for receiving God's forgiviness.

I believe the thought of Hebrews and Paul suggest this.

Lamarr