When Adam and Eve sinned in the Garden of Eden, God pronounced a sentence: “You must surely die.” He was speaking of their spiritual death, which came immediately, and also of their physical death, which came about because of sin. In the Old Testament Law, God made temporary provision for sin. A specified animal could be sacrificed in place of the person who committed the sin. According to Hebrews 10:1-17, these sacrifices merely postponed the consequences of the sin until Jesus, the perfect sacrifice, would be offered to completely atone for the sin.
The animal sacrifices also gave a clear picture of the atonement that was to come, acting as a teaching tool to show Israel the consequences of their sin. God was the only One who was a perfect sacrifice to atone for the sin. He accomplished this by dying himself in the person of Jesus Christ.