Lev 1:5-6, Lev 17:11, Rom 3:25
To protect Adam and Eve, sinners, God slaughtered animals and made clothes with skins and clothed them. This implies that Christ will be sacrificed for us. (Genesis 3:21)
Genesis 3:21 Unto Adam also and to his wife did the Lord God make coats of skins, and clothed them.
In the Old Testament, God allowed the blood of animals to be shed for the sins of the Israelites to be forgiven. (Lev 1:5, Lev 17:11)
Lev 1:5 And he shall kill the bullock before the Lord: and the priests, Aaron's sons, shall bring the blood, and sprinkle the blood round about upon the altar that is by the door of the tabernacle of the congregation.
Lev 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.
Jesus became the propitiation sacrifice to forgive our sins. (Romans 3:25)
Romans 3:25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God;