The Bible makes no apologies for the emphasis on the blood. In the Garden of Eden after the first sin, a blood sacrifice was exacted to provide the animal skins for clothing for Adam and Eve. When Cain and Abel made offerings to God, Abel's was accepted but Cain's was not because he did not provide the blood sacrifice. In Genesis Abraham built altars everywhere he went. He knew the meaning of sacrifice. He was called by God to sacrifice his son Isaac. He went to Mount Moriah with the intent to sacrifice his son there. When God withdrew the command to kill Isaac, Abraham took the ram caught in the bushes to make the sacrifice. The substitute was accepted and Isaac was spared.
In Exodus 12 God gave the requirement for the Passover to Moses.
The sacrifice must be a lamb 1 year old, without spot or blemish. You cannot sacrifice an animal that you would have cut from the flock anyway. Sacrifice means it will cost you. In the case of Abraham's sacrifice, he didn't have to sacrifice Isaac, but in his heart he had committed him to God. The Passover Lamb was the acceptable substitute for the sins of the people of Israel.
In Leviticus 17:11 the Bible proclaims that the life of a creature is in the blood. God gave the blood to make the sacrifice; it was not for food. The Law forbade the eating of blood. Animals killed for meat were to be drained of blood and the blood was offered on the altar.
Jesus came as an innocent sacrifice and his blood was spilled at Calvary. He was our substitute like the ram was a substitute for Isaac on Mount Moriah and the lamb was a substitute for Israel on the Day of Atonement. Jesus did not stop with the sacrifice, but his resurrection assures us of life in him when we accept his sacrifice for ourselves.