Question: "Why did the sacrificial system require a blood sacrifice?"
Answer: The whole of the Old Testament, every book, points toward the Great Sacrifice that was to come—that of Jesus’ sacrificial giving of His own life on our behalf. Leviticus 17:11 is the Old Testament’s central statement about the significance of blood in the sacrificial system. God, speaking to Moses, declares: “For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life.”
A “sacrifice” is defined as the offering up of something precious for a cause or a reason. Making atonement is satisfying someone or something for an offense committed. The Leviticus verse can be read more clearly now: God said, “I have given it to you (the creature’s life, which is in its blood) to make atonement for yourselves (covering the offense you have committed against Me).” In other words, those who are covered by the blood sacrifice are set free from the consequences of sin.
Of course, the Israelites did not know of Jesus per se, or how He would die on their behalf and then rise again, but they did believe God would be sending them a Savior. All of the many, many blood sacrifices seen throughout the Old Testament were foreshadowing the true, once-for-all-time sacrifice to come so that the Israelites would never forget that, without the blood, there is no forgiveness. This shedding of blood is a substitutionary act. Therefore, the last clause of Leviticus 17:11 could be read either “the blood ‘makes atonement’ at the cost of the life” (i.e., the animal’s life) or “makes atonement in the place of the life” (i.e., the sinner’s life, with Jesus Christ being the One giving life through His shed blood).
Hebrews 9:11-18 confirms the symbolism of blood as life and applies Leviticus 17:11 to the sacrifice of the Lord Jesus Christ. Verse 12 states clearly that the Old Testament blood sacrifices were temporary and only atoned for sin partially and for a short time, hence the need to repeat the sacrifices yearly. But when Christ entered the Most Holy Place, He did so to offer His own blood once for all time, making future sacrifices unnecessary. This is what Jesus meant by His dying words on the cross: “It is finished” (John 19:30). Never again would the blood of bulls and goats cleanse men from their sin. Only by accepting Jesus’ blood, shed on the cross for the remission of sins, can we stand before God covered in the righteousness of Christ (2 Corinthians 5:21).