How did things change between the Old and New Testaments?
One of the biggest changes between the Old and New Covenants is how sin was handled.
In the Old Covenant, God established the priesthood to provide a way for the Israelites to cover or atone for sin—the breaking of the law. The high priest offered a blood sacrifice each year in the Holy of Holies to cover the sins of the people. When the high priest failed, the people had no approach to God.
In contrast, the blood of Jesus did not just cover over our sins; it eradicated our sins.