God has never treated sin lightly because he has always desired to have people reconciled to Himself. Sin can be cured only on the ground of the shed blood of the Son of God. This was true of those who anticipated the death of Christ by animal sacrifices as it is now of those who look back to that death by faith.

Under the old covenant sin was only covered by the blood of animals (Heb 10:4), however it was once and for all removed by Jesus Christ (John 1:29, Col 2:14).

For further study on this you can read "Major bible Themes" by Lewis Sperry Chafer, chapter 28 (Salvation from the penalty of sin).