Genesis 22: 13
...Abraham went and took the ram, and offered it up for a burnt offering in the place of his son.
This is a very specific and obvious substitution of the animal for the person's death. This was before the Law was given.
We see since Adam and Eve that the death of an animal was to substitute for the death of the person, as God clothed them with the animals' hides.
God has always taught His people this principle, which He later codified in the Law He gave to Moses. The very first sacrifice a person was to offer was the personal, individual one, listed first in Leviticus, the book of sacrifices. The person brought his own animal to the priest, laid his hand on the animal's head to identify with it, and the priest would then kill it, burn it on the altar, and splash its blood on the sides of the altar. This blood would cover the person's sins, and they could be forgiven.
This lays out what Jesus came to accomplish, and He fulfilled all the Law, including the sacrifices. Jesus died in the place of each of us, individually, when we admit to God that we deserve death and let Him be our personal Sacrifice, His blood splashed on the sides of His altar, the Cross.
God does not change. He required a death from the very beginning, because "the wages of sin is death" (Romans 6:23), so each of us deserves to die.
That's how much He loves us. God planned from before He created, to have Jesus be the Sacrifice to take away our sins, to make us fit to live with Him forever. From the Garden of Eden to Abraham's offering of Isaac, to the Law, to Jesus fulfilling all the letter of the Law. We don't offer animal sacrifices any more, because Jesus died "once for all" (I Peter 3:18). No more blood sacrifices will ever need to be made, since Jesus fulfilled that requirement for all time.
Even so, come, Lord Jesus!
