Adam and Eve wanted to become God. They sinned and passed the buck by not taking responsibility and as a result, God kicked man out of the garden and cursed the earth where sin entered the world. The Bible also talks about enmity in several places. King James Bible Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. https://biblehub.com/romans/8-7.htm A couple of things happened between Genesis and Romans. Man sinned and offended a holy God, there was violence on the earth where God had to push reset with the flood and now we have enmity with God. Lots of Christians get offended because I tell them I think they are still at enmity with God. Why do we have to die? Because sin entered the human race and God said flesh and blood will not inherit the kingdom of heaven. Why do we have to have punishment? There are consequences for knowing good and evil. It wasn't God's plan for us to sin. As a result, God could not have let man eat of the tree of life so he appointed angels to guard the tree of life with flaming swords. Why? Because if they ate of the tree of life, I just postulate that man would have lived in a sinful condition forever. The other thing is that the kingdom of darkness is involved and God's honor is at stake. Its also the reality that we have the wrong master in the flesh and we have to die to have the right master. In a sense, bad things have to happen to us for us to look to God. Because its a fight, it involves the kingdom of darkness. The kingdom of light has worth and majesty. What is the worth of God? Will a sacrifice of animals make it up to God? Will burning some toast as a sacrifice make things up to God? I don't have to have the answers. Its just the way it works because we were made in the image of God and now Adam's children were made in Adam's image and the image of sin. In order to get back to God, we have to be born from above which involves God putting His life and his nature back into us. That is basically the plan and part of the program. In order for us to get back to God, it follows this program of getting God's righteousness through not only the shed blood of Jesus but applying it to our souls which involves Jesus paying our ransom. There is no salvation without blood atonement in this relationship with God.
Part 2. As a result of sin, I have to pay daily. I want the bad angels to pay, I want Satan to pay and I'm want some of the heathens to pay. Ok? Hold that thought. The Navigators have this example. I'm a good person because I only sin once a day? Right? 70 years X 365 days = 25,550 sins. We all know I sin more than once a day. This is the problem of evil. I unintentionally hurt people. I've done wrong. For God to get rid of all the evil, God would have to get rid of you and me but because God wants people to be redeemed, some of his strong actions have to be saved so that He doesn't damage our thoughts about Him to keep us from coming to get redeemed by God by coming to Him. God doesn't want to damage the wheat which is us in the parable. Justice involves a price and righteousness has weight. God is also going to get rid of the evil one day and we can decide where we want to be. We can decide for God to take our evil upon Himself and punish it or we can keep our evil. The reason why some don't want to believe in God is because God allows evil thing to happen so they don't think God is just. But because God is going to put away the evil and because God is just, there must be a payment for sin. Just saying you are sorry and getting forgiven does not pay restitution and the atheist that doesn't believe in God because God allows evil, it requires justice for the atheist to believe in God because the athiest's conscience which is given by God demands justice..
And yet God ordered animal sacrifice for sin. So basically it comes down to the same question, why the need for death and blood while he forgave the Jewish nation zillions of times without.
Sacrifice is one way of cleansing sin. But it's not sort sort of "magic" and it isn't about punishing the animal. It's a vehicle for the sinner. Let's think; I sin accidentally. So now I have to take something of value to me, something that feeds me and my family, and gift it to God. I have to make the long journey to Jerusalem. I have to go to the Temple, and lean on the animal and confess my sin. Because I wasn't careful, this poor animal has to die. So I should be more careful in the future. And the bible gives many other vehicles for forgiveness ; Charity and good deeds come to mind immediately. In fact, sacrifice only works for accidental or inadvertent sin. Intentional sin has no sacrifice. See numbers 15: "But anyone who sins defiantly, whether native-born or foreigner, blasphemes the LORD and must be cut off from the people of Israel." No sacrifice. The very next passage is about the Sabbath violator, who is put to death for his sin. No sacrifice.