In The Book Of Romans, Paul wrote,
Romans 5:12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned.
When man sinned in the Garden, death entered. It is logical, then, that for man to overcome death, He must remove sin from his life. The problem is that death did a thorough work on man through his sin. The result of our first parent's sin was man's spirit being separated from God's fellowship, never being able to come to union with Him because of his sin. How, then could man find restoration? God has spoken clearly in His word and has told us that the way to reconciliation with Him is through the shedding of blood. But not just any blood sacrifice will do. That which would be sacrificed must be perfect to atone for the perfect, yet innocent, life Adam slew in the Garden: his own, and that of all of his offspring who would come forth from him. This was man's dilemma: Adam's race could only bring forth imperfect life, sinful life that was separated from God and would never serve as a sacrifice for sin. God, therefore, had to provide man with the sacrifice he could not produce, and He did that by sending Jesus to become our sin offering.
God's way of atonement is given in Leviticus 17:
Leviticus 17:11 For the life of the flesh is in the blood: and I have given it to you upon the altar to make an atonement for your souls: for it is the blood that maketh an atonement for the soul.
The writer to the Hebrews makes this plain, telling us that without the shedding of blood there is no remission of sin:
Hebrews 9:18 Whereupon neither the first testament was dedicated without blood.
The shedding of the blood of animals, though, did not contain the fulness of what God wanted to tell humanity concerning the shedding of Blood for the atonement and cleansing of sin, as the writer to the Hebrews explains:
Hebrews 10:4 For it is not possible that the blood of bulls and of goats should take away sins.
Just as the Old Covenant was initiated by the shedding of the blood of animals, so the New Covenant was initiated by the shedding of the blood of Jesus, the Son of God:
Hebrews 10:5 Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
God wanted humanity to know He had the perfect sacrifice for them and forshadowed that sacrifice by the animals slain in the Old Testament. The blood of animals in the Old Testament had to be shed continually to deal with the sins of the people, but Jesus was sacrificed ONLY ONCE for all men:
Hebrews 7:26 For such an high priest became us, who is holy, harmless, undefiled, separate from sinners, and made higher than the heavens;
Hebrews 9:28 So Christ WAS ONCE OFFERED to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.
Hebrews 10:10 By the which will we are sanctified through the offering of the body of Jesus Christ ONCE FOR ALL.
God has established the one sacrifice for the atonement and cleansing of sin, and that can be received by all men through faith in what Jesus Christ, God's Son, did on Calvary.