How do we know atonement is true in the Bible?

The concept of atonement is central to the Old Testament sacrificial system, which was a temporary covering for sin, depicted in the Day of Atonement rituals. The New Testament reveals that these sacrifices were merely shadows of the ultimate and perfect atonement achieved through Christ's death. Hebrews 9:11-12 explains that Christ entered the holy place and offered His own blood for eternal redemption, demonstrating that His sacrifice fulfilled the law and provided a permanent solution for sin—contrary to the temporary coverings of the Old Testament.